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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/nexgen32e/crc32init.S Normal file
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/*-*- mode:asm; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
│vi: set et ft=asm ts=8 tw=8 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/macros.h"
.text.startup
/ Generates lookup table for computing CRC-32 byte-by-byte.
/
/ void crc32init(uint32_t table[256], uint32_t polynomial) {
/ uint32_t d, i, r;
/ for (d = 0; d < 256; ++d) {
/ r = d;
/ for (i = 0; i < 8; ++i) {
/ r = r >> 1 ^ (r & 1 ? polynomial : 0);
/ }
/ table[d] = r;
/ }
/ }
/
/ @param rdi is pointer to uint32_t[256] array
/ @param esi 32-bit binary polynomial config
/ @note imposes ~300ns one-time cost
crc32init:
push %rbp
mov %rsp,%rbp
.profilable
lea 256*4(%rdi),%rdx
movd %esi,%xmm0
pshufd $0,%xmm0,%xmm0 # (uint32_t[]){esi,esi,esi,esi} → %xmm0
pushpop 4,%rax
movd %eax,%xmm2 # (int[]){4,4,4,4} → %xmm2
pshufd $0,%xmm2,%xmm2
0: sub $4,%rsp # (int[]){0,1,2,3} → %xmm1
dec %eax
mov %eax,(%rsp)
jnz 0b
movups (%rsp),%xmm1
1: mov $8,%ecx
movdqa %xmm1,%xmm3
2: movdqa %xmm3,%xmm4
psrld $1,%xmm4
pslld $31,%xmm3
psrad $31,%xmm3
pand %xmm0,%xmm3
pxor %xmm4,%xmm3
movdqa %xmm3,%xmm4
loop 2b
movdqu %xmm3,(%rdi)
add $16,%rdi
paddd %xmm2,%xmm1
cmp %rdx,%rdi
jb 1b
leave
ret
.endfn crc32init,globl
.yoink __FILE__