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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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libc/nexgen32e/strstr.inc 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 sw=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 │
╚─────────────────────────────────────────────────────────────────────────────*/
/* clang-format off */
/ Searches for substring.
/
/ @param rdi is NUL-terminated haystack string
/ @param rsi is NUL-terminated needle string (16-byte aligned)
/ @return rax is pointer to substring or NULL
/ @todo 10x faster than naïve but could be 100x faster
.macro .strstr mode:req
push %rbp
mov %rsp,%rbp
.profilable
sub $32,%rsp
mov %rdi,%rax
xor %ecx,%ecx
0: mov $-16,%rdx
1: add $16,%rdx
movaps (%rsi,%rdx),%xmm0
2: add %rcx,%rax
lea (%rax,%rdx),%rdi
test $15,%edi
jnz 6f
pcmpistri $\mode,(%rdi),%xmm0
3: ja 2b # !CF (no match) && !ZF (need NUL-term)
jnc 4f # !CF (no match) && ZF (NUL-terminator)
jno 0b # !OF ← CF && CX!=0 (matched at offset)
jns 1b # !SF ← NUL ∉ XMM1 (need to match more)
jmp 5f # youtu.be/nVk1DjMtLWs
4: xor %eax,%eax
5: leave
ret
6: mov %rdi,%r9 # same w/ pointer realign
and $15,%r9d
mov %edi,%r8d
and $0xfff,%r8d
cmp $0xff0,%r8d
ja 8f
7: pcmpistri $\mode,(%rdi),%xmm0
cmova %r9d,%ecx
jmp 3b
8: pcmpeqd %xmm2,%xmm2 # handle danger memory
mov %rdi,%r8
and $-16,%r8
movaps (%r8),%xmm1
movaps %xmm1,-32(%rbp)
movaps %xmm2,-16(%rbp)
pcmpistri $\mode,-32(%rbp,%r9),%xmm2
jz 4b
jmp 7b
.endm