Date: Fri, 8 Sep 2023 21:23:34 GMT From: Robert Clausecker <fuz@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: de12a689fad2 - main - lib/libc/amd64/string: add memchr(3) scalar, baseline implementation Message-ID: <202309082123.388LNYdv057537@gitrepo.freebsd.org>
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The branch main has been updated by fuz: URL: https://cgit.FreeBSD.org/src/commit/?id=de12a689fad271f5a2ba7c188b0b5fb5cabf48e7 commit de12a689fad271f5a2ba7c188b0b5fb5cabf48e7 Author: Robert Clausecker <fuz@FreeBSD.org> AuthorDate: 2023-08-24 16:43:40 +0000 Commit: Robert Clausecker <fuz@FreeBSD.org> CommitDate: 2023-09-08 21:22:20 +0000 lib/libc/amd64/string: add memchr(3) scalar, baseline implementation This is conceptually similar to strchr(3), but there are slight changes to account for the buffer having an explicit buffer length. Sponsored by: The FreeBSD Foundation Approved by: mjg MFC after: 1 week MFC to: stable/14 Differential Revision: https://reviews.freebsd.org/D41598 --- lib/libc/amd64/string/Makefile.inc | 1 + lib/libc/amd64/string/memchr.S | 204 +++++++++++++++++++++++++++++++++++++ 2 files changed, 205 insertions(+) diff --git a/lib/libc/amd64/string/Makefile.inc b/lib/libc/amd64/string/Makefile.inc index b03811f40062..7c6a1f429590 100644 --- a/lib/libc/amd64/string/Makefile.inc +++ b/lib/libc/amd64/string/Makefile.inc @@ -2,6 +2,7 @@ MDSRCS+= \ amd64_archlevel.c \ bcmp.S \ + memchr.S \ memcmp.S \ memcpy.S \ memmove.S \ diff --git a/lib/libc/amd64/string/memchr.S b/lib/libc/amd64/string/memchr.S new file mode 100644 index 000000000000..e10bd6c22f90 --- /dev/null +++ b/lib/libc/amd64/string/memchr.S @@ -0,0 +1,204 @@ +/*- + * Copyright (c) 2023 The FreeBSD Foundation + * + * This software was developed by Robert Clausecker <fuz@FreeBSD.org> + * under sponsorship from the FreeBSD Foundation. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ''AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE + */ + +#include <machine/asm.h> + +#include "amd64_archlevel.h" + +#define ALIGN_TEXT .p2align 4,0x90 /* 16-byte alignment, nop filled */ + + .weak memchr + .set memchr, __memchr +ARCHFUNCS(__memchr) + ARCHFUNC(__memchr, scalar) + ARCHFUNC(__memchr, baseline) +ENDARCHFUNCS(__memchr) + +ARCHENTRY(__memchr, scalar) + test %rdx, %rdx # empty input? + je .Lnomatch + + lea (, %rdi, 8), %ecx + add %rdi, %rdx # pointer to end of buffer + and $~7, %rdi # align to 8 bytes + mov (%rdi), %rax # load first word + movzbl %sil, %esi # clear stray high bits + movabs $0x0101010101010101, %r8 + imul %r8, %rsi # replicate char 8 times + + /* compute head and tail masks */ + mov %r8, %r10 + movabs $0x8080808080808080, %r9 + shl %cl, %r10 # 0x01 where string head is + lea (, %rdx, 8), %ecx + xor %r8, %r10 # 0x01 where it is not + neg %r8 # negate 01..01 so we can use lea + mov %r9, %r11 + xor %rsi, %rax # str ^ c (0x00 where str[i] == c) + neg %ecx + or %r10, %rax # except before the string + shr %cl, %r11 # 0x80 where string tail is + + add $8, %rdi # advance to next 8 bytes + cmp %rdx, %rdi # end of buffer reached during head? + jae .Ltail # and go to tail-processing code + + /* main loop, unrolled twice */ + ALIGN_TEXT +0: lea (%rax, %r8, 1), %rcx # (str ^ c) - 0x01..01 + not %rax # ~(str ^ c) + and %r9, %rax # ((str^c) - 0x01..01) & ~(str^c) + and %rcx, %rax # not including junk bytes + jnz .Lmatch + + mov (%rdi), %rax + add $8, %rdi + xor %rsi, %rax # str ^ c + cmp %rdx, %rdi + jae .Ltail + + lea (%rax, %r8, 1), %rcx # (str ^ c) - 0x01..01 + not %rax # ~(str ^ c) + and %r9, %rax # ((str^c) - 0x01..01) & ~(str^c) + and %rcx, %rax # not including junk bytes + jnz .Lmatch + + mov (%rdi), %rax + add $8, %rdi + xor %rsi, %rax # str ^ c + cmp %rdx, %rdi + jb 0b + +.Ltail: lea (%rax, %r8, 1), %rcx # (str ^ c) - 0x01..01 + not %rax # ~(str ^ c) + and %r11, %rax # ((str^c) - 0x01..01) & ~(str^c) + and %rcx, %rax # not including junk bytes or bytes past buffer + jz .Lnomatch + +.Lmatch: + tzcnt %rax, %rax # first match + shr $3, %eax # scale from bit to byte index + lea -8(%rdi, %rax), %rax # pointer to found c + ret + + /* no match found */ +.Lnomatch: + xor %eax, %eax # return null pointer + ret +ARCHEND(__memchr, scalar) + +ARCHENTRY(__memchr, baseline) + test %rdx, %rdx # empty input? + je .Lnomatchb + + movd %esi, %xmm2 + mov %edi, %ecx + add %rdi, %rdx # pointer to end of buffer + and $~0x1f, %rdi # align to 32 bytes + movdqa (%rdi), %xmm0 # load first 32 bytes + movdqa 16(%rdi), %xmm1 + + punpcklbw %xmm2, %xmm2 # c -> cc + + mov $-1, %r9d + shl %cl, %r9d # mask with zeroes before the string + + punpcklwd %xmm2, %xmm2 # cc -> cccc + + mov $-1, %r8d + xor %ecx, %ecx + sub %edx, %ecx # edx = -ecx + shr %cl, %r8d # bytes in tail that are part of the buffer + + pshufd $0, %xmm2, %xmm2 # cccc -> cccccccccccccccc + + add $32, %rdi # advance to next 32 bytes + mov $-1, %eax + cmp %rdx, %rdi # end of buffer reached during head? + cmovae %r8d, %eax # if yes, do combined head/tail processing + and %r9d, %eax # mask of bytes in head part of string + + /* process head */ + pcmpeqb %xmm2, %xmm1 + pcmpeqb %xmm2, %xmm0 + pmovmskb %xmm1, %esi + pmovmskb %xmm0, %ecx + shl $16, %esi + or %esi, %ecx # locations of matches + and %ecx, %eax # any match inside buffer? + jnz .Lprecisematchb + + cmp %rdx, %rdi # did the buffer end here? + jae .Lnomatchb # if yes we are done + + /* main loop */ + ALIGN_TEXT +0: movdqa (%rdi), %xmm0 # load next string chunk + movdqa 16(%rdi), %xmm1 + add $32, %rdi + cmp %rdx, %rdi # ready for main loop? + jae .Ltailb + + pcmpeqb %xmm2, %xmm0 + pcmpeqb %xmm2, %xmm1 + por %xmm1, %xmm0 # match in either half? + pmovmskb %xmm0, %eax + test %eax, %eax + jz 0b + +.Lmatchb: + pcmpeqb -32(%rdi), %xmm2 # redo comparison of first 16 bytes + pmovmskb %xmm1, %ecx + pmovmskb %xmm2, %eax + shl $16, %ecx + or %ecx, %eax # location of matches + +.Lprecisematchb: + tzcnt %eax, %eax # find location of match + lea -32(%rdi, %rax, 1), %rax # point to matching byte + ret + +.Ltailb: + pcmpeqb %xmm2, %xmm1 + pcmpeqb %xmm2, %xmm0 + pmovmskb %xmm1, %edx + pmovmskb %xmm0, %eax + shl $16, %edx + or %edx, %eax # location of matches + and %r8d, %eax # mask out matches beyond buffer + bsf %eax, %edx # location of match + lea -32(%rdi, %rdx, 1), %rdx # pointer to match (if any) + cmovnz %rdx, %rax # point to match if present, + ret # else null pointer + +.Lnomatchb: + xor %eax, %eax # return null pointer + ret +ARCHEND(__memchr, baseline) + + .section .note.GNU-stack,"",%progbits
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