1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
use core::iter::{FromIterator, Iterator};
use core::mem::{self, ManuallyDrop};
use core::ops::{Deref, DerefMut};
use core::ptr::{self, NonNull};
use core::{cmp, fmt, hash, isize, slice, usize};

use alloc::{
    borrow::{Borrow, BorrowMut},
    boxed::Box,
    string::String,
    vec::Vec,
};

use crate::buf::{IntoIter, UninitSlice};
use crate::bytes::Vtable;
#[allow(unused)]
use crate::loom::sync::atomic::AtomicMut;
use crate::loom::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
use crate::{Buf, BufMut, Bytes};

/// A unique reference to a contiguous slice of memory.
///
/// `BytesMut` represents a unique view into a potentially shared memory region.
/// Given the uniqueness guarantee, owners of `BytesMut` handles are able to
/// mutate the memory.
///
/// `BytesMut` can be thought of as containing a `buf: Arc<Vec<u8>>`, an offset
/// into `buf`, a slice length, and a guarantee that no other `BytesMut` for the
/// same `buf` overlaps with its slice. That guarantee means that a write lock
/// is not required.
///
/// # Growth
///
/// `BytesMut`'s `BufMut` implementation will implicitly grow its buffer as
/// necessary. However, explicitly reserving the required space up-front before
/// a series of inserts will be more efficient.
///
/// # Examples
///
/// ```
/// use bytes::{BytesMut, BufMut};
///
/// let mut buf = BytesMut::with_capacity(64);
///
/// buf.put_u8(b'h');
/// buf.put_u8(b'e');
/// buf.put(&b"llo"[..]);
///
/// assert_eq!(&buf[..], b"hello");
///
/// // Freeze the buffer so that it can be shared
/// let a = buf.freeze();
///
/// // This does not allocate, instead `b` points to the same memory.
/// let b = a.clone();
///
/// assert_eq!(&a[..], b"hello");
/// assert_eq!(&b[..], b"hello");
/// ```
pub struct BytesMut {
    ptr: NonNull<u8>,
    len: usize,
    cap: usize,
    data: *mut Shared,
}

// Thread-safe reference-counted container for the shared storage. This mostly
// the same as `core::sync::Arc` but without the weak counter. The ref counting
// fns are based on the ones found in `std`.
//
// The main reason to use `Shared` instead of `core::sync::Arc` is that it ends
// up making the overall code simpler and easier to reason about. This is due to
// some of the logic around setting `Inner::arc` and other ways the `arc` field
// is used. Using `Arc` ended up requiring a number of funky transmutes and
// other shenanigans to make it work.
struct Shared {
    vec: Vec<u8>,
    original_capacity_repr: usize,
    ref_count: AtomicUsize,
}

// Buffer storage strategy flags.
const KIND_ARC: usize = 0b0;
const KIND_VEC: usize = 0b1;
const KIND_MASK: usize = 0b1;

// The max original capacity value. Any `Bytes` allocated with a greater initial
// capacity will default to this.
const MAX_ORIGINAL_CAPACITY_WIDTH: usize = 17;
// The original capacity algorithm will not take effect unless the originally
// allocated capacity was at least 1kb in size.
const MIN_ORIGINAL_CAPACITY_WIDTH: usize = 10;
// The original capacity is stored in powers of 2 starting at 1kb to a max of
// 64kb. Representing it as such requires only 3 bits of storage.
const ORIGINAL_CAPACITY_MASK: usize = 0b11100;
const ORIGINAL_CAPACITY_OFFSET: usize = 2;

// When the storage is in the `Vec` representation, the pointer can be advanced
// at most this value. This is due to the amount of storage available to track
// the offset is usize - number of KIND bits and number of ORIGINAL_CAPACITY
// bits.
const VEC_POS_OFFSET: usize = 5;
const MAX_VEC_POS: usize = usize::MAX >> VEC_POS_OFFSET;
const NOT_VEC_POS_MASK: usize = 0b11111;

#[cfg(target_pointer_width = "64")]
const PTR_WIDTH: usize = 64;
#[cfg(target_pointer_width = "32")]
const PTR_WIDTH: usize = 32;

/*
 *
 * ===== BytesMut =====
 *
 */

impl BytesMut {
    /// Creates a new `BytesMut` with the specified capacity.
    ///
    /// The returned `BytesMut` will be able to hold at least `capacity` bytes
    /// without reallocating.
    ///
    /// It is important to note that this function does not specify the length
    /// of the returned `BytesMut`, but only the capacity.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut bytes = BytesMut::with_capacity(64);
    ///
    /// // `bytes` contains no data, even though there is capacity
    /// assert_eq!(bytes.len(), 0);
    ///
    /// bytes.put(&b"hello world"[..]);
    ///
    /// assert_eq!(&bytes[..], b"hello world");
    /// ```
    #[inline]
    pub fn with_capacity(capacity: usize) -> BytesMut {
        BytesMut::from_vec(Vec::with_capacity(capacity))
    }

    /// Creates a new `BytesMut` with default capacity.
    ///
    /// Resulting object has length 0 and unspecified capacity.
    /// This function does not allocate.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut bytes = BytesMut::new();
    ///
    /// assert_eq!(0, bytes.len());
    ///
    /// bytes.reserve(2);
    /// bytes.put_slice(b"xy");
    ///
    /// assert_eq!(&b"xy"[..], &bytes[..]);
    /// ```
    #[inline]
    pub fn new() -> BytesMut {
        BytesMut::with_capacity(0)
    }

    /// Returns the number of bytes contained in this `BytesMut`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::from(&b"hello"[..]);
    /// assert_eq!(b.len(), 5);
    /// ```
    #[inline]
    pub fn len(&self) -> usize {
        self.len
    }

    /// Returns true if the `BytesMut` has a length of 0.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::with_capacity(64);
    /// assert!(b.is_empty());
    /// ```
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len == 0
    }

    /// Returns the number of bytes the `BytesMut` can hold without reallocating.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let b = BytesMut::with_capacity(64);
    /// assert_eq!(b.capacity(), 64);
    /// ```
    #[inline]
    pub fn capacity(&self) -> usize {
        self.cap
    }

    /// Converts `self` into an immutable `Bytes`.
    ///
    /// The conversion is zero cost and is used to indicate that the slice
    /// referenced by the handle will no longer be mutated. Once the conversion
    /// is done, the handle can be cloned and shared across threads.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    /// use std::thread;
    ///
    /// let mut b = BytesMut::with_capacity(64);
    /// b.put(&b"hello world"[..]);
    /// let b1 = b.freeze();
    /// let b2 = b1.clone();
    ///
    /// let th = thread::spawn(move || {
    ///     assert_eq!(&b1[..], b"hello world");
    /// });
    ///
    /// assert_eq!(&b2[..], b"hello world");
    /// th.join().unwrap();
    /// ```
    #[inline]
    pub fn freeze(mut self) -> Bytes {
        if self.kind() == KIND_VEC {
            // Just re-use `Bytes` internal Vec vtable
            unsafe {
                let (off, _) = self.get_vec_pos();
                let vec = rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off);
                mem::forget(self);
                let mut b: Bytes = vec.into();
                b.advance(off);
                b
            }
        } else {
            debug_assert_eq!(self.kind(), KIND_ARC);

            let ptr = self.ptr.as_ptr();
            let len = self.len;
            let data = AtomicPtr::new(self.data as _);
            mem::forget(self);
            unsafe { Bytes::with_vtable(ptr, len, data, &SHARED_VTABLE) }
        }
    }

    /// Splits the bytes into two at the given index.
    ///
    /// Afterwards `self` contains elements `[0, at)`, and the returned
    /// `BytesMut` contains elements `[at, capacity)`.
    ///
    /// This is an `O(1)` operation that just increases the reference count
    /// and sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut a = BytesMut::from(&b"hello world"[..]);
    /// let mut b = a.split_off(5);
    ///
    /// a[0] = b'j';
    /// b[0] = b'!';
    ///
    /// assert_eq!(&a[..], b"jello");
    /// assert_eq!(&b[..], b"!world");
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if `at > capacity`.
    #[must_use = "consider BytesMut::truncate if you don't need the other half"]
    pub fn split_off(&mut self, at: usize) -> BytesMut {
        assert!(
            at <= self.capacity(),
            "split_off out of bounds: {:?} <= {:?}",
            at,
            self.capacity(),
        );
        unsafe {
            let mut other = self.shallow_clone();
            other.set_start(at);
            self.set_end(at);
            other
        }
    }

    /// Removes the bytes from the current view, returning them in a new
    /// `BytesMut` handle.
    ///
    /// Afterwards, `self` will be empty, but will retain any additional
    /// capacity that it had before the operation. This is identical to
    /// `self.split_to(self.len())`.
    ///
    /// This is an `O(1)` operation that just increases the reference count and
    /// sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut buf = BytesMut::with_capacity(1024);
    /// buf.put(&b"hello world"[..]);
    ///
    /// let other = buf.split();
    ///
    /// assert!(buf.is_empty());
    /// assert_eq!(1013, buf.capacity());
    ///
    /// assert_eq!(other, b"hello world"[..]);
    /// ```
    #[must_use = "consider BytesMut::advance(len()) if you don't need the other half"]
    pub fn split(&mut self) -> BytesMut {
        let len = self.len();
        self.split_to(len)
    }

    /// Splits the buffer into two at the given index.
    ///
    /// Afterwards `self` contains elements `[at, len)`, and the returned `BytesMut`
    /// contains elements `[0, at)`.
    ///
    /// This is an `O(1)` operation that just increases the reference count and
    /// sets a few indices.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut a = BytesMut::from(&b"hello world"[..]);
    /// let mut b = a.split_to(5);
    ///
    /// a[0] = b'!';
    /// b[0] = b'j';
    ///
    /// assert_eq!(&a[..], b"!world");
    /// assert_eq!(&b[..], b"jello");
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if `at > len`.
    #[must_use = "consider BytesMut::advance if you don't need the other half"]
    pub fn split_to(&mut self, at: usize) -> BytesMut {
        assert!(
            at <= self.len(),
            "split_to out of bounds: {:?} <= {:?}",
            at,
            self.len(),
        );

        unsafe {
            let mut other = self.shallow_clone();
            other.set_end(at);
            self.set_start(at);
            other
        }
    }

    /// Shortens the buffer, keeping the first `len` bytes and dropping the
    /// rest.
    ///
    /// If `len` is greater than the buffer's current length, this has no
    /// effect.
    ///
    /// The [`split_off`] method can emulate `truncate`, but this causes the
    /// excess bytes to be returned instead of dropped.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello world"[..]);
    /// buf.truncate(5);
    /// assert_eq!(buf, b"hello"[..]);
    /// ```
    ///
    /// [`split_off`]: #method.split_off
    pub fn truncate(&mut self, len: usize) {
        if len <= self.len() {
            unsafe {
                self.set_len(len);
            }
        }
    }

    /// Clears the buffer, removing all data.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello world"[..]);
    /// buf.clear();
    /// assert!(buf.is_empty());
    /// ```
    pub fn clear(&mut self) {
        self.truncate(0);
    }

    /// Resizes the buffer so that `len` is equal to `new_len`.
    ///
    /// If `new_len` is greater than `len`, the buffer is extended by the
    /// difference with each additional byte set to `value`. If `new_len` is
    /// less than `len`, the buffer is simply truncated.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::new();
    ///
    /// buf.resize(3, 0x1);
    /// assert_eq!(&buf[..], &[0x1, 0x1, 0x1]);
    ///
    /// buf.resize(2, 0x2);
    /// assert_eq!(&buf[..], &[0x1, 0x1]);
    ///
    /// buf.resize(4, 0x3);
    /// assert_eq!(&buf[..], &[0x1, 0x1, 0x3, 0x3]);
    /// ```
    pub fn resize(&mut self, new_len: usize, value: u8) {
        let len = self.len();
        if new_len > len {
            let additional = new_len - len;
            self.reserve(additional);
            unsafe {
                let dst = self.chunk_mut().as_mut_ptr();
                ptr::write_bytes(dst, value, additional);
                self.set_len(new_len);
            }
        } else {
            self.truncate(new_len);
        }
    }

    /// Sets the length of the buffer.
    ///
    /// This will explicitly set the size of the buffer without actually
    /// modifying the data, so it is up to the caller to ensure that the data
    /// has been initialized.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut b = BytesMut::from(&b"hello world"[..]);
    ///
    /// unsafe {
    ///     b.set_len(5);
    /// }
    ///
    /// assert_eq!(&b[..], b"hello");
    ///
    /// unsafe {
    ///     b.set_len(11);
    /// }
    ///
    /// assert_eq!(&b[..], b"hello world");
    /// ```
    #[inline]
    pub unsafe fn set_len(&mut self, len: usize) {
        debug_assert!(len <= self.cap, "set_len out of bounds");
        self.len = len;
    }

    /// Reserves capacity for at least `additional` more bytes to be inserted
    /// into the given `BytesMut`.
    ///
    /// More than `additional` bytes may be reserved in order to avoid frequent
    /// reallocations. A call to `reserve` may result in an allocation.
    ///
    /// Before allocating new buffer space, the function will attempt to reclaim
    /// space in the existing buffer. If the current handle references a small
    /// view in the original buffer and all other handles have been dropped,
    /// and the requested capacity is less than or equal to the existing
    /// buffer's capacity, then the current view will be copied to the front of
    /// the buffer and the handle will take ownership of the full buffer.
    ///
    /// # Examples
    ///
    /// In the following example, a new buffer is allocated.
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::from(&b"hello"[..]);
    /// buf.reserve(64);
    /// assert!(buf.capacity() >= 69);
    /// ```
    ///
    /// In the following example, the existing buffer is reclaimed.
    ///
    /// ```
    /// use bytes::{BytesMut, BufMut};
    ///
    /// let mut buf = BytesMut::with_capacity(128);
    /// buf.put(&[0; 64][..]);
    ///
    /// let ptr = buf.as_ptr();
    /// let other = buf.split();
    ///
    /// assert!(buf.is_empty());
    /// assert_eq!(buf.capacity(), 64);
    ///
    /// drop(other);
    /// buf.reserve(128);
    ///
    /// assert_eq!(buf.capacity(), 128);
    /// assert_eq!(buf.as_ptr(), ptr);
    /// ```
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `usize`.
    #[inline]
    pub fn reserve(&mut self, additional: usize) {
        let len = self.len();
        let rem = self.capacity() - len;

        if additional <= rem {
            // The handle can already store at least `additional` more bytes, so
            // there is no further work needed to be done.
            return;
        }

        self.reserve_inner(additional);
    }

    // In separate function to allow the short-circuits in `reserve` to
    // be inline-able. Significant helps performance.
    fn reserve_inner(&mut self, additional: usize) {
        let len = self.len();
        let kind = self.kind();

        if kind == KIND_VEC {
            // If there's enough free space before the start of the buffer, then
            // just copy the data backwards and reuse the already-allocated
            // space.
            //
            // Otherwise, since backed by a vector, use `Vec::reserve`
            unsafe {
                let (off, prev) = self.get_vec_pos();

                // Only reuse space if we can satisfy the requested additional space.
                if self.capacity() - self.len() + off >= additional {
                    // There's space - reuse it
                    //
                    // Just move the pointer back to the start after copying
                    // data back.
                    let base_ptr = self.ptr.as_ptr().offset(-(off as isize));
                    ptr::copy(self.ptr.as_ptr(), base_ptr, self.len);
                    self.ptr = vptr(base_ptr);
                    self.set_vec_pos(0, prev);

                    // Length stays constant, but since we moved backwards we
                    // can gain capacity back.
                    self.cap += off;
                } else {
                    // No space - allocate more
                    let mut v =
                        ManuallyDrop::new(rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off));
                    v.reserve(additional);

                    // Update the info
                    self.ptr = vptr(v.as_mut_ptr().offset(off as isize));
                    self.len = v.len() - off;
                    self.cap = v.capacity() - off;
                }

                return;
            }
        }

        debug_assert_eq!(kind, KIND_ARC);
        let shared: *mut Shared = self.data as _;

        // Reserving involves abandoning the currently shared buffer and
        // allocating a new vector with the requested capacity.
        //
        // Compute the new capacity
        let mut new_cap = len.checked_add(additional).expect("overflow");

        let original_capacity;
        let original_capacity_repr;

        unsafe {
            original_capacity_repr = (*shared).original_capacity_repr;
            original_capacity = original_capacity_from_repr(original_capacity_repr);

            // First, try to reclaim the buffer. This is possible if the current
            // handle is the only outstanding handle pointing to the buffer.
            if (*shared).is_unique() {
                // This is the only handle to the buffer. It can be reclaimed.
                // However, before doing the work of copying data, check to make
                // sure that the vector has enough capacity.
                let v = &mut (*shared).vec;

                if v.capacity() >= new_cap {
                    // The capacity is sufficient, reclaim the buffer
                    let ptr = v.as_mut_ptr();

                    ptr::copy(self.ptr.as_ptr(), ptr, len);

                    self.ptr = vptr(ptr);
                    self.cap = v.capacity();

                    return;
                }

                // The vector capacity is not sufficient. The reserve request is
                // asking for more than the initial buffer capacity. Allocate more
                // than requested if `new_cap` is not much bigger than the current
                // capacity.
                //
                // There are some situations, using `reserve_exact` that the
                // buffer capacity could be below `original_capacity`, so do a
                // check.
                let double = v.capacity().checked_shl(1).unwrap_or(new_cap);

                new_cap = cmp::max(cmp::max(double, new_cap), original_capacity);
            } else {
                new_cap = cmp::max(new_cap, original_capacity);
            }
        }

        // Create a new vector to store the data
        let mut v = ManuallyDrop::new(Vec::with_capacity(new_cap));

        // Copy the bytes
        v.extend_from_slice(self.as_ref());

        // Release the shared handle. This must be done *after* the bytes are
        // copied.
        unsafe { release_shared(shared) };

        // Update self
        let data = (original_capacity_repr << ORIGINAL_CAPACITY_OFFSET) | KIND_VEC;
        self.data = data as _;
        self.ptr = vptr(v.as_mut_ptr());
        self.len = v.len();
        self.cap = v.capacity();
    }

    /// Appends given bytes to this `BytesMut`.
    ///
    /// If this `BytesMut` object does not have enough capacity, it is resized
    /// first.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::with_capacity(0);
    /// buf.extend_from_slice(b"aaabbb");
    /// buf.extend_from_slice(b"cccddd");
    ///
    /// assert_eq!(b"aaabbbcccddd", &buf[..]);
    /// ```
    pub fn extend_from_slice(&mut self, extend: &[u8]) {
        let cnt = extend.len();
        self.reserve(cnt);

        unsafe {
            let dst = self.uninit_slice();
            // Reserved above
            debug_assert!(dst.len() >= cnt);

            ptr::copy_nonoverlapping(extend.as_ptr(), dst.as_mut_ptr() as *mut u8, cnt);
        }

        unsafe {
            self.advance_mut(cnt);
        }
    }

    /// Absorbs a `BytesMut` that was previously split off.
    ///
    /// If the two `BytesMut` objects were previously contiguous, i.e., if
    /// `other` was created by calling `split_off` on this `BytesMut`, then
    /// this is an `O(1)` operation that just decreases a reference
    /// count and sets a few indices. Otherwise this method degenerates to
    /// `self.extend_from_slice(other.as_ref())`.
    ///
    /// # Examples
    ///
    /// ```
    /// use bytes::BytesMut;
    ///
    /// let mut buf = BytesMut::with_capacity(64);
    /// buf.extend_from_slice(b"aaabbbcccddd");
    ///
    /// let split = buf.split_off(6);
    /// assert_eq!(b"aaabbb", &buf[..]);
    /// assert_eq!(b"cccddd", &split[..]);
    ///
    /// buf.unsplit(split);
    /// assert_eq!(b"aaabbbcccddd", &buf[..]);
    /// ```
    pub fn unsplit(&mut self, other: BytesMut) {
        if self.is_empty() {
            *self = other;
            return;
        }

        if let Err(other) = self.try_unsplit(other) {
            self.extend_from_slice(other.as_ref());
        }
    }

    // private

    // For now, use a `Vec` to manage the memory for us, but we may want to
    // change that in the future to some alternate allocator strategy.
    //
    // Thus, we don't expose an easy way to construct from a `Vec` since an
    // internal change could make a simple pattern (`BytesMut::from(vec)`)
    // suddenly a lot more expensive.
    #[inline]
    pub(crate) fn from_vec(mut vec: Vec<u8>) -> BytesMut {
        let ptr = vptr(vec.as_mut_ptr());
        let len = vec.len();
        let cap = vec.capacity();
        mem::forget(vec);

        let original_capacity_repr = original_capacity_to_repr(cap);
        let data = (original_capacity_repr << ORIGINAL_CAPACITY_OFFSET) | KIND_VEC;

        BytesMut {
            ptr,
            len,
            cap,
            data: data as *mut _,
        }
    }

    #[inline]
    fn as_slice(&self) -> &[u8] {
        unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) }
    }

    #[inline]
    fn as_slice_mut(&mut self) -> &mut [u8] {
        unsafe { slice::from_raw_parts_mut(self.ptr.as_ptr(), self.len) }
    }

    unsafe fn set_start(&mut self, start: usize) {
        // Setting the start to 0 is a no-op, so return early if this is the
        // case.
        if start == 0 {
            return;
        }

        debug_assert!(start <= self.cap, "internal: set_start out of bounds");

        let kind = self.kind();

        if kind == KIND_VEC {
            // Setting the start when in vec representation is a little more
            // complicated. First, we have to track how far ahead the
            // "start" of the byte buffer from the beginning of the vec. We
            // also have to ensure that we don't exceed the maximum shift.
            let (mut pos, prev) = self.get_vec_pos();
            pos += start;

            if pos <= MAX_VEC_POS {
                self.set_vec_pos(pos, prev);
            } else {
                // The repr must be upgraded to ARC. This will never happen
                // on 64 bit systems and will only happen on 32 bit systems
                // when shifting past 134,217,727 bytes. As such, we don't
                // worry too much about performance here.
                self.promote_to_shared(/*ref_count = */ 1);
            }
        }

        // Updating the start of the view is setting `ptr` to point to the
        // new start and updating the `len` field to reflect the new length
        // of the view.
        self.ptr = vptr(self.ptr.as_ptr().offset(start as isize));

        if self.len >= start {
            self.len -= start;
        } else {
            self.len = 0;
        }

        self.cap -= start;
    }

    unsafe fn set_end(&mut self, end: usize) {
        debug_assert_eq!(self.kind(), KIND_ARC);
        assert!(end <= self.cap, "set_end out of bounds");

        self.cap = end;
        self.len = cmp::min(self.len, end);
    }

    fn try_unsplit(&mut self, other: BytesMut) -> Result<(), BytesMut> {
        if other.is_empty() {
            return Ok(());
        }

        let ptr = unsafe { self.ptr.as_ptr().offset(self.len as isize) };
        if ptr == other.ptr.as_ptr()
            && self.kind() == KIND_ARC
            && other.kind() == KIND_ARC
            && self.data == other.data
        {
            // Contiguous blocks, just combine directly
            self.len += other.len;
            self.cap += other.cap;
            Ok(())
        } else {
            Err(other)
        }
    }

    #[inline]
    fn kind(&self) -> usize {
        self.data as usize & KIND_MASK
    }

    unsafe fn promote_to_shared(&mut self, ref_cnt: usize) {
        debug_assert_eq!(self.kind(), KIND_VEC);
        debug_assert!(ref_cnt == 1 || ref_cnt == 2);

        let original_capacity_repr =
            (self.data as usize & ORIGINAL_CAPACITY_MASK) >> ORIGINAL_CAPACITY_OFFSET;

        // The vec offset cannot be concurrently mutated, so there
        // should be no danger reading it.
        let off = (self.data as usize) >> VEC_POS_OFFSET;

        // First, allocate a new `Shared` instance containing the
        // `Vec` fields. It's important to note that `ptr`, `len`,
        // and `cap` cannot be mutated without having `&mut self`.
        // This means that these fields will not be concurrently
        // updated and since the buffer hasn't been promoted to an
        // `Arc`, those three fields still are the components of the
        // vector.
        let shared = Box::new(Shared {
            vec: rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off),
            original_capacity_repr,
            ref_count: AtomicUsize::new(ref_cnt),
        });

        let shared = Box::into_raw(shared);

        // The pointer should be aligned, so this assert should
        // always succeed.
        debug_assert_eq!(shared as usize & KIND_MASK, KIND_ARC);

        self.data = shared as _;
    }

    /// Makes an exact shallow clone of `self`.
    ///
    /// The kind of `self` doesn't matter, but this is unsafe
    /// because the clone will have the same offsets. You must
    /// be sure the returned value to the user doesn't allow
    /// two views into the same range.
    #[inline]
    unsafe fn shallow_clone(&mut self) -> BytesMut {
        if self.kind() == KIND_ARC {
            increment_shared(self.data);
            ptr::read(self)
        } else {
            self.promote_to_shared(/*ref_count = */ 2);
            ptr::read(self)
        }
    }

    #[inline]
    unsafe fn get_vec_pos(&mut self) -> (usize, usize) {
        debug_assert_eq!(self.kind(), KIND_VEC);

        let prev = self.data as usize;
        (prev >> VEC_POS_OFFSET, prev)
    }

    #[inline]
    unsafe fn set_vec_pos(&mut self, pos: usize, prev: usize) {
        debug_assert_eq!(self.kind(), KIND_VEC);
        debug_assert!(pos <= MAX_VEC_POS);

        self.data = ((pos << VEC_POS_OFFSET) | (prev & NOT_VEC_POS_MASK)) as *mut _;
    }

    #[inline]
    fn uninit_slice(&mut self) -> &mut UninitSlice {
        unsafe {
            let ptr = self.ptr.as_ptr().offset(self.len as isize);
            let len = self.cap - self.len;

            UninitSlice::from_raw_parts_mut(ptr, len)
        }
    }
}

impl Drop for BytesMut {
    fn drop(&mut self) {
        let kind = self.kind();

        if kind == KIND_VEC {
            unsafe {
                let (off, _) = self.get_vec_pos();

                // Vector storage, free the vector
                let _ = rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off);
            }
        } else if kind == KIND_ARC {
            unsafe { release_shared(self.data as _) };
        }
    }
}

impl Buf for BytesMut {
    #[inline]
    fn remaining(&self) -> usize {
        self.len()
    }

    #[inline]
    fn chunk(&self) -> &[u8] {
        self.as_slice()
    }

    #[inline]
    fn advance(&mut self, cnt: usize) {
        assert!(
            cnt <= self.remaining(),
            "cannot advance past `remaining`: {:?} <= {:?}",
            cnt,
            self.remaining(),
        );
        unsafe {
            self.set_start(cnt);
        }
    }

    fn copy_to_bytes(&mut self, len: usize) -> crate::Bytes {
        self.split_to(len).freeze()
    }
}

unsafe impl BufMut for BytesMut {
    #[inline]
    fn remaining_mut(&self) -> usize {
        usize::MAX - self.len()
    }

    #[inline]
    unsafe fn advance_mut(&mut self, cnt: usize) {
        let new_len = self.len() + cnt;
        assert!(
            new_len <= self.cap,
            "new_len = {}; capacity = {}",
            new_len,
            self.cap
        );
        self.len = new_len;
    }

    #[inline]
    fn chunk_mut(&mut self) -> &mut UninitSlice {
        if self.capacity() == self.len() {
            self.reserve(64);
        }
        self.uninit_slice()
    }

    // Specialize these methods so they can skip checking `remaining_mut`
    // and `advance_mut`.

    fn put<T: crate::Buf>(&mut self, mut src: T)
    where
        Self: Sized,
    {
        while src.has_remaining() {
            let s = src.chunk();
            let l = s.len();
            self.extend_from_slice(s);
            src.advance(l);
        }
    }

    fn put_slice(&mut self, src: &[u8]) {
        self.extend_from_slice(src);
    }
}

impl AsRef<[u8]> for BytesMut {
    #[inline]
    fn as_ref(&self) -> &[u8] {
        self.as_slice()
    }
}

impl Deref for BytesMut {
    type Target = [u8];

    #[inline]
    fn deref(&self) -> &[u8] {
        self.as_ref()
    }
}

impl AsMut<[u8]> for BytesMut {
    #[inline]
    fn as_mut(&mut self) -> &mut [u8] {
        self.as_slice_mut()
    }
}

impl DerefMut for BytesMut {
    #[inline]
    fn deref_mut(&mut self) -> &mut [u8] {
        self.as_mut()
    }
}

impl<'a> From<&'a [u8]> for BytesMut {
    fn from(src: &'a [u8]) -> BytesMut {
        BytesMut::from_vec(src.to_vec())
    }
}

impl<'a> From<&'a str> for BytesMut {
    fn from(src: &'a str) -> BytesMut {
        BytesMut::from(src.as_bytes())
    }
}

impl From<BytesMut> for Bytes {
    fn from(src: BytesMut) -> Bytes {
        src.freeze()
    }
}

impl PartialEq for BytesMut {
    fn eq(&self, other: &BytesMut) -> bool {
        self.as_slice() == other.as_slice()
    }
}

impl PartialOrd for BytesMut {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        self.as_slice().partial_cmp(other.as_slice())
    }
}

impl Ord for BytesMut {
    fn cmp(&self, other: &BytesMut) -> cmp::Ordering {
        self.as_slice().cmp(other.as_slice())
    }
}

impl Eq for BytesMut {}

impl Default for BytesMut {
    #[inline]
    fn default() -> BytesMut {
        BytesMut::new()
    }
}

impl hash::Hash for BytesMut {
    fn hash<H>(&self, state: &mut H)
    where
        H: hash::Hasher,
    {
        let s: &[u8] = self.as_ref();
        s.hash(state);
    }
}

impl Borrow<[u8]> for BytesMut {
    fn borrow(&self) -> &[u8] {
        self.as_ref()
    }
}

impl BorrowMut<[u8]> for BytesMut {
    fn borrow_mut(&mut self) -> &mut [u8] {
        self.as_mut()
    }
}

impl fmt::Write for BytesMut {
    #[inline]
    fn write_str(&mut self, s: &str) -> fmt::Result {
        if self.remaining_mut() >= s.len() {
            self.put_slice(s.as_bytes());
            Ok(())
        } else {
            Err(fmt::Error)
        }
    }

    #[inline]
    fn write_fmt(&mut self, args: fmt::Arguments<'_>) -> fmt::Result {
        fmt::write(self, args)
    }
}

impl Clone for BytesMut {
    fn clone(&self) -> BytesMut {
        BytesMut::from(&self[..])
    }
}

impl IntoIterator for BytesMut {
    type Item = u8;
    type IntoIter = IntoIter<BytesMut>;

    fn into_iter(self) -> Self::IntoIter {
        IntoIter::new(self)
    }
}

impl<'a> IntoIterator for &'a BytesMut {
    type Item = &'a u8;
    type IntoIter = core::slice::Iter<'a, u8>;

    fn into_iter(self) -> Self::IntoIter {
        self.as_ref().into_iter()
    }
}

impl Extend<u8> for BytesMut {
    fn extend<T>(&mut self, iter: T)
    where
        T: IntoIterator<Item = u8>,
    {
        let iter = iter.into_iter();

        let (lower, _) = iter.size_hint();
        self.reserve(lower);

        // TODO: optimize
        // 1. If self.kind() == KIND_VEC, use Vec::extend
        // 2. Make `reserve` inline-able
        for b in iter {
            self.reserve(1);
            self.put_u8(b);
        }
    }
}

impl<'a> Extend<&'a u8> for BytesMut {
    fn extend<T>(&mut self, iter: T)
    where
        T: IntoIterator<Item = &'a u8>,
    {
        self.extend(iter.into_iter().map(|b| *b))
    }
}

impl FromIterator<u8> for BytesMut {
    fn from_iter<T: IntoIterator<Item = u8>>(into_iter: T) -> Self {
        BytesMut::from_vec(Vec::from_iter(into_iter))
    }
}

impl<'a> FromIterator<&'a u8> for BytesMut {
    fn from_iter<T: IntoIterator<Item = &'a u8>>(into_iter: T) -> Self {
        BytesMut::from_iter(into_iter.into_iter().map(|b| *b))
    }
}

/*
 *
 * ===== Inner =====
 *
 */

unsafe fn increment_shared(ptr: *mut Shared) {
    let old_size = (*ptr).ref_count.fetch_add(1, Ordering::Relaxed);

    if old_size > isize::MAX as usize {
        crate::abort();
    }
}

unsafe fn release_shared(ptr: *mut Shared) {
    // `Shared` storage... follow the drop steps from Arc.
    if (*ptr).ref_count.fetch_sub(1, Ordering::Release) != 1 {
        return;
    }

    // This fence is needed to prevent reordering of use of the data and
    // deletion of the data.  Because it is marked `Release`, the decreasing
    // of the reference count synchronizes with this `Acquire` fence. This
    // means that use of the data happens before decreasing the reference
    // count, which happens before this fence, which happens before the
    // deletion of the data.
    //
    // As explained in the [Boost documentation][1],
    //
    // > It is important to enforce any possible access to the object in one
    // > thread (through an existing reference) to *happen before* deleting
    // > the object in a different thread. This is achieved by a "release"
    // > operation after dropping a reference (any access to the object
    // > through this reference must obviously happened before), and an
    // > "acquire" operation before deleting the object.
    //
    // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
    atomic::fence(Ordering::Acquire);

    // Drop the data
    Box::from_raw(ptr);
}

impl Shared {
    fn is_unique(&self) -> bool {
        // The goal is to check if the current handle is the only handle
        // that currently has access to the buffer. This is done by
        // checking if the `ref_count` is currently 1.
        //
        // The `Acquire` ordering synchronizes with the `Release` as
        // part of the `fetch_sub` in `release_shared`. The `fetch_sub`
        // operation guarantees that any mutations done in other threads
        // are ordered before the `ref_count` is decremented. As such,
        // this `Acquire` will guarantee that those mutations are
        // visible to the current thread.
        self.ref_count.load(Ordering::Acquire) == 1
    }
}

fn original_capacity_to_repr(cap: usize) -> usize {
    let width = PTR_WIDTH - ((cap >> MIN_ORIGINAL_CAPACITY_WIDTH).leading_zeros() as usize);
    cmp::min(
        width,
        MAX_ORIGINAL_CAPACITY_WIDTH - MIN_ORIGINAL_CAPACITY_WIDTH,
    )
}

fn original_capacity_from_repr(repr: usize) -> usize {
    if repr == 0 {
        return 0;
    }

    1 << (repr + (MIN_ORIGINAL_CAPACITY_WIDTH - 1))
}

/*
#[test]
fn test_original_capacity_to_repr() {
    assert_eq!(original_capacity_to_repr(0), 0);

    let max_width = 32;

    for width in 1..(max_width + 1) {
        let cap = 1 << width - 1;

        let expected = if width < MIN_ORIGINAL_CAPACITY_WIDTH {
            0
        } else if width < MAX_ORIGINAL_CAPACITY_WIDTH {
            width - MIN_ORIGINAL_CAPACITY_WIDTH
        } else {
            MAX_ORIGINAL_CAPACITY_WIDTH - MIN_ORIGINAL_CAPACITY_WIDTH
        };

        assert_eq!(original_capacity_to_repr(cap), expected);

        if width > 1 {
            assert_eq!(original_capacity_to_repr(cap + 1), expected);
        }

        //  MIN_ORIGINAL_CAPACITY_WIDTH must be bigger than 7 to pass tests below
        if width == MIN_ORIGINAL_CAPACITY_WIDTH + 1 {
            assert_eq!(original_capacity_to_repr(cap - 24), expected - 1);
            assert_eq!(original_capacity_to_repr(cap + 76), expected);
        } else if width == MIN_ORIGINAL_CAPACITY_WIDTH + 2 {
            assert_eq!(original_capacity_to_repr(cap - 1), expected - 1);
            assert_eq!(original_capacity_to_repr(cap - 48), expected - 1);
        }
    }
}

#[test]
fn test_original_capacity_from_repr() {
    assert_eq!(0, original_capacity_from_repr(0));

    let min_cap = 1 << MIN_ORIGINAL_CAPACITY_WIDTH;

    assert_eq!(min_cap, original_capacity_from_repr(1));
    assert_eq!(min_cap * 2, original_capacity_from_repr(2));
    assert_eq!(min_cap * 4, original_capacity_from_repr(3));
    assert_eq!(min_cap * 8, original_capacity_from_repr(4));
    assert_eq!(min_cap * 16, original_capacity_from_repr(5));
    assert_eq!(min_cap * 32, original_capacity_from_repr(6));
    assert_eq!(min_cap * 64, original_capacity_from_repr(7));
}
*/

unsafe impl Send for BytesMut {}
unsafe impl Sync for BytesMut {}

/*
 *
 * ===== PartialEq / PartialOrd =====
 *
 */

impl PartialEq<[u8]> for BytesMut {
    fn eq(&self, other: &[u8]) -> bool {
        &**self == other
    }
}

impl PartialOrd<[u8]> for BytesMut {
    fn partial_cmp(&self, other: &[u8]) -> Option<cmp::Ordering> {
        (**self).partial_cmp(other)
    }
}

impl PartialEq<BytesMut> for [u8] {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for [u8] {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self, other)
    }
}

impl PartialEq<str> for BytesMut {
    fn eq(&self, other: &str) -> bool {
        &**self == other.as_bytes()
    }
}

impl PartialOrd<str> for BytesMut {
    fn partial_cmp(&self, other: &str) -> Option<cmp::Ordering> {
        (**self).partial_cmp(other.as_bytes())
    }
}

impl PartialEq<BytesMut> for str {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for str {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self.as_bytes(), other)
    }
}

impl PartialEq<Vec<u8>> for BytesMut {
    fn eq(&self, other: &Vec<u8>) -> bool {
        *self == &other[..]
    }
}

impl PartialOrd<Vec<u8>> for BytesMut {
    fn partial_cmp(&self, other: &Vec<u8>) -> Option<cmp::Ordering> {
        (**self).partial_cmp(&other[..])
    }
}

impl PartialEq<BytesMut> for Vec<u8> {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for Vec<u8> {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        other.partial_cmp(self)
    }
}

impl PartialEq<String> for BytesMut {
    fn eq(&self, other: &String) -> bool {
        *self == &other[..]
    }
}

impl PartialOrd<String> for BytesMut {
    fn partial_cmp(&self, other: &String) -> Option<cmp::Ordering> {
        (**self).partial_cmp(other.as_bytes())
    }
}

impl PartialEq<BytesMut> for String {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for String {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self.as_bytes(), other)
    }
}

impl<'a, T: ?Sized> PartialEq<&'a T> for BytesMut
where
    BytesMut: PartialEq<T>,
{
    fn eq(&self, other: &&'a T) -> bool {
        *self == **other
    }
}

impl<'a, T: ?Sized> PartialOrd<&'a T> for BytesMut
where
    BytesMut: PartialOrd<T>,
{
    fn partial_cmp(&self, other: &&'a T) -> Option<cmp::Ordering> {
        self.partial_cmp(*other)
    }
}

impl PartialEq<BytesMut> for &[u8] {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for &[u8] {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        <[u8] as PartialOrd<[u8]>>::partial_cmp(self, other)
    }
}

impl PartialEq<BytesMut> for &str {
    fn eq(&self, other: &BytesMut) -> bool {
        *other == *self
    }
}

impl PartialOrd<BytesMut> for &str {
    fn partial_cmp(&self, other: &BytesMut) -> Option<cmp::Ordering> {
        other.partial_cmp(self)
    }
}

impl PartialEq<BytesMut> for Bytes {
    fn eq(&self, other: &BytesMut) -> bool {
        &other[..] == &self[..]
    }
}

impl PartialEq<Bytes> for BytesMut {
    fn eq(&self, other: &Bytes) -> bool {
        &other[..] == &self[..]
    }
}

fn vptr(ptr: *mut u8) -> NonNull<u8> {
    if cfg!(debug_assertions) {
        NonNull::new(ptr).expect("Vec pointer should be non-null")
    } else {
        unsafe { NonNull::new_unchecked(ptr) }
    }
}

unsafe fn rebuild_vec(ptr: *mut u8, mut len: usize, mut cap: usize, off: usize) -> Vec<u8> {
    let ptr = ptr.offset(-(off as isize));
    len += off;
    cap += off;

    Vec::from_raw_parts(ptr, len, cap)
}

// ===== impl SharedVtable =====

static SHARED_VTABLE: Vtable = Vtable {
    clone: shared_v_clone,
    drop: shared_v_drop,
};

unsafe fn shared_v_clone(data: &AtomicPtr<()>, ptr: *const u8, len: usize) -> Bytes {
    let shared = data.load(Ordering::Relaxed) as *mut Shared;
    increment_shared(shared);

    let data = AtomicPtr::new(shared as _);
    Bytes::with_vtable(ptr, len, data, &SHARED_VTABLE)
}

unsafe fn shared_v_drop(data: &mut AtomicPtr<()>, _ptr: *const u8, _len: usize) {
    data.with_mut(|shared| {
        release_shared(*shared as *mut Shared);
    });
}

// compile-fails

/// ```compile_fail
/// use bytes::BytesMut;
/// #[deny(unused_must_use)]
/// {
///     let mut b1 = BytesMut::from("hello world");
///     b1.split_to(6);
/// }
/// ```
fn _split_to_must_use() {}

/// ```compile_fail
/// use bytes::BytesMut;
/// #[deny(unused_must_use)]
/// {
///     let mut b1 = BytesMut::from("hello world");
///     b1.split_off(6);
/// }
/// ```
fn _split_off_must_use() {}

/// ```compile_fail
/// use bytes::BytesMut;
/// #[deny(unused_must_use)]
/// {
///     let mut b1 = BytesMut::from("hello world");
///     b1.split();
/// }
/// ```
fn _split_must_use() {}

// fuzz tests
#[cfg(all(test, loom))]
mod fuzz {
    use loom::sync::Arc;
    use loom::thread;

    use super::BytesMut;
    use crate::Bytes;

    #[test]
    fn bytes_mut_cloning_frozen() {
        loom::model(|| {
            let a = BytesMut::from(&b"abcdefgh"[..]).split().freeze();
            let addr = a.as_ptr() as usize;

            // test the Bytes::clone is Sync by putting it in an Arc
            let a1 = Arc::new(a);
            let a2 = a1.clone();

            let t1 = thread::spawn(move || {
                let b: Bytes = (*a1).clone();
                assert_eq!(b.as_ptr() as usize, addr);
            });

            let t2 = thread::spawn(move || {
                let b: Bytes = (*a2).clone();
                assert_eq!(b.as_ptr() as usize, addr);
            });

            t1.join().unwrap();
            t2.join().unwrap();
        });
    }
}