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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/nexgen32e/crc32c-pure.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/str/internal.h"
/**
* Computes Castagnoli CRC-32 on old computers.
*/
uint32_t crc32c$pure(uint32_t init, const void *data, size_t size) {
extern const uint32_t kCrc32cTab[256];
const unsigned char *p = data;
uint32_t h = init ^ 0xffffffff;
unsigned i;
for (i = 0; i < size; i++) {
h = h >> 8 ^ kCrc32cTab[(h & 0xff) ^ p[i]];
}
return h ^ 0xffffffff;
}
/*
bench_crc32c$pure for #c per n where c ≈ 0.293ns
N x1 x8 x64 mBps
------------------------------------------------------------
1 4305.000 91.375 44.203 74
1 75.000 55.875 44.703 73
2 46.500 35.188 24.617 132
3 40.333 26.625 19.193 169
4 32.250 19.969 16.215 200
7 18.429 15.089 12.033 270
8 20.625 13.547 11.607 280
15 15.667 10.775 9.589 339
16 17.562 10.695 9.419 345
31 12.226 8.891 8.317 391
32 13.219 8.480 8.078 402
63 9.571 8.065 7.731 420
64 9.672 7.955 7.633 426
127 8.433 7.548 7.329 443
128 8.492 7.528 7.352 442
255 7.557 7.366 7.239 449
256 7.699 7.342 7.305 445
511 7.376 7.243 7.223 450
512 7.408 7.233 7.225 450
1023 7.188 7.192 7.098 458
1024 7.171 7.194 7.097 458
2047 7.130 7.172 7.085 459
2048 7.117 7.170 7.169 453
4095 7.063 7.076 7.085 459
4096 7.078 7.161 7.081 459
8191 7.041 7.095 7.055 461
8192 7.051 7.098 7.087 459
16383 7.039 7.114 7.067 460
16384 6.876 6.931 7.133 456
32767 7.055 7.108 7.290 446
32768 6.868 6.887 6.974 466
65535 6.984 6.885 6.967 467
65536 6.877 6.924 10.994 296
131071 7.166 7.141 7.011 464
131072 6.853 6.971 7.694 422
262143 6.853 7.213 7.406 439
262144 6.852 6.968 7.290 446
524287 7.398 7.389 7.166 454
524288 6.851 7.094 7.159 454
*/