Date: Wed, 24 Jan 2024 19:44:36 GMT From: Robert Clausecker <fuz@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 9b1a851e1ed0 - stable/14 - lib/libc/amd64/string: add strrchr scalar, baseline implementation Message-ID: <202401241944.40OJiaFv005127@gitrepo.freebsd.org>
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The branch stable/14 has been updated by fuz: URL: https://cgit.FreeBSD.org/src/commit/?id=9b1a851e1ed04d38736011c227e8f9494acec681 commit 9b1a851e1ed04d38736011c227e8f9494acec681 Author: Robert Clausecker <fuz@FreeBSD.org> AuthorDate: 2023-10-12 05:37:41 +0000 Commit: Robert Clausecker <fuz@FreeBSD.org> CommitDate: 2024-01-24 19:39:26 +0000 lib/libc/amd64/string: add strrchr scalar, baseline implementation The baseline implementation is very straightforward, while the scalar implementation suffers from register pressure and the need to use SWAR techniques similar to those used for strchr(). Sponsored by: The FreeBSD Foundation Tested by: developers@, exp-run Approved by: mjg MFC after: 1 month MFC to: stable/14 PR: 275785 Differential Revision: https://reviews.freebsd.org/D42217 (cherry picked from commit 2ed514a220edbac6ca5ec9f40a3e0b3f2804796d) --- lib/libc/amd64/string/Makefile.inc | 1 + lib/libc/amd64/string/strrchr.S | 209 +++++++++++++++++++++++++++++++++++++ 2 files changed, 210 insertions(+) diff --git a/lib/libc/amd64/string/Makefile.inc b/lib/libc/amd64/string/Makefile.inc index 51645ba3b8af..2baa631fb3fa 100644 --- a/lib/libc/amd64/string/Makefile.inc +++ b/lib/libc/amd64/string/Makefile.inc @@ -16,6 +16,7 @@ MDSRCS+= \ strncmp.S \ strnlen.c \ strpbrk.c \ + strrchr.S \ strspn.S \ timingsafe_bcmp.S \ timingsafe_memcmp.S diff --git a/lib/libc/amd64/string/strrchr.S b/lib/libc/amd64/string/strrchr.S new file mode 100644 index 000000000000..e397bbcd3478 --- /dev/null +++ b/lib/libc/amd64/string/strrchr.S @@ -0,0 +1,209 @@ +/*- + * 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 rindex + .set rindex, strrchr + +ARCHFUNCS(strrchr) + ARCHFUNC(strrchr, scalar) + ARCHFUNC(strrchr, baseline) +ENDARCHFUNCS(strrchr) + +ARCHENTRY(strrchr, scalar) + mov %edi, %ecx + and $~7, %rdi # align to 8 byte + movzbl %sil, %esi # clear stray high bits + movabs $0x0101010101010101, %r8 + mov (%rdi), %rax # load first word + imul %r8, %rsi # replicate char 8 times + + /* + * Unaligned input: align to 8 bytes. Then proceed the same + * way as with aligned input, but prevent matches before the + * beginning of the string. This is achieved by oring 0x01 + * into each byte of the buffer before the string + */ + shl $3, %ecx + mov %r8, %r10 + shl %cl, %r10 # 0x01 where the string is + xor %r8, %r10 # 0x01 where it is not + neg %r8 # negate 01..01 so we can use lea + movabs $0x8080808080808080, %r9 + + mov %rsi, %rcx + xor %rax, %rcx # str ^ c + or %r10, %rax # ensure str != 0 before string + or %r10, %rcx # ensure str^c != 0 before string + bswap %rcx # in reverse order, to find last match + mov %rdi, %r10 # location of initial mismatch (if any) + xor %r11, %r11 # initial mismatch (none) + add $8, %rdi # advance to next iteration + lea (%rax, %r8, 1), %rdx # str - 0x01..01 + not %rax # ~str + and %rdx, %rax # (str - 0x01..01) & ~str + and %r9, %rax # not including junk bits + jnz 1f # end of string? + + lea (%rcx, %r8, 1), %rdx # (str ^ c) - 0x01..01 + not %rcx # ~(str ^ c) + and %rdx, %rcx # ((str ^ c - 0x01..01) & ~(str ^ c) + and %r9, %rcx # not including junk bits + mov %rcx, %r11 # remember mismatch in head + jmp 0f + + /* main loop unrolled twice */ + ALIGN_TEXT +3: lea (%rcx, %r8, 1), %rdx # (str ^ c) - 0x01..01 + not %rcx # ~(str ^ c) + and %rdx, %rcx # ((str ^ c - 0x01..01) & ~(str ^ c) + and %r9, %rcx # not including junk bits + lea -8(%rdi), %rdx + cmovnz %rdx, %r10 # remember location of current mismatch + cmovnz %rcx, %r11 + +0: mov (%rdi), %rax # str + mov %rsi, %rcx + xor %rax, %rcx # str ^ c + bswap %rcx # in reverse order, to find last match + lea (%rax, %r8, 1), %rdx # str - 0x01..01 + not %rax # ~str + and %rdx, %rax # (str - 0x01..01) & ~str + and %r9, %rax # not including junk bits + jnz 2f # end of string? + + lea (%rcx, %r8, 1), %rdx # (str ^ c) - 0x01..01 + not %rcx # ~(str ^ c) + and %rdx, %rcx # ((str ^ c - 0x01..01) & ~(str ^ c) + and %r9, %rcx # not including junk bits + cmovnz %rdi, %r10 # remember location of current mismatch + cmovnz %rcx, %r11 + + mov 8(%rdi), %rax # str + add $16, %rdi + mov %rsi, %rcx + xor %rax, %rcx # str ^ c + bswap %rcx + lea (%rax, %r8, 1), %rdx # str - 0x01..01 + not %rax # ~str + and %rdx, %rax # (str - 0x01..01) & ~str + and %r9, %rax # not including junk bits + jz 3b # end of string? + + /* NUL found */ +1: sub $8, %rdi # undo advance past buffer +2: lea (%rcx, %r8, 1), %rdx # (str ^ c) - 0x01..01 + not %rcx # ~(str ^ c) + and %rdx, %rcx # ((str ^ c - 0x01..01) & ~(str ^ c) + and %r9, %rcx # not including junk bits + lea -1(%rax), %rdx + xor %rdx, %rax # mask of bytes in the string + bswap %rdx # in reverse order + and %rdx, %rcx # c found in the tail? + cmovnz %rdi, %r10 + cmovnz %rcx, %r11 + bswap %r11 # unreverse byte order + bsr %r11, %rcx # last location of c in (R10) + shr $3, %rcx # as byte offset + lea (%r10, %rcx, 1), %rax # pointer to match + test %r11, %r11 # was there actually a match? + cmovz %r11, %rax # if not, return null pointer + ret +ARCHEND(strrchr, scalar) + +ARCHENTRY(strrchr, baseline) + mov %edi, %ecx + and $~0xf, %rdi # align to 16 bytes + movdqa (%rdi), %xmm1 + movd %esi, %xmm0 + and $0xf, %ecx # offset from alignment + pxor %xmm2, %xmm2 + mov $-1, %edx + punpcklbw %xmm0, %xmm0 # c -> cc + shl %cl, %edx # bits corresponding to bytes in the string + punpcklwd %xmm0, %xmm0 # cc -> cccc + xor %r8, %r8 # address of latest match + mov $1, %esi # bit mask of latest match + mov %rdi, %r9 # candidate location for next match + add $16, %rdi # advance to next chunk + + /* check for match in head */ + pcmpeqb %xmm1, %xmm2 # NUL byte present? + pshufd $0, %xmm0, %xmm0 # cccc -> cccccccccccccccc + pcmpeqb %xmm0, %xmm1 # c present? + pmovmskb %xmm2, %eax + pmovmskb %xmm1, %ecx + and %edx, %ecx # c present in the string? + and %edx, %eax # NUL present in the string? + jnz .Lend2 + + /* main loop unrolled twice */ + ALIGN_TEXT +0: movdqa (%rdi), %xmm1 + test %ecx, %ecx # was there a match in the last iter.? + cmovnz %r9, %r8 # remember match if any + cmovnz %ecx, %esi + pxor %xmm2, %xmm2 + pcmpeqb %xmm1, %xmm2 # NUL byte present? + pcmpeqb %xmm0, %xmm1 # c present? + pmovmskb %xmm2, %eax + pmovmskb %xmm1, %ecx + test %eax, %eax # end of string in first half? + jnz .Lend + + movdqa 16(%rdi), %xmm1 + test %ecx, %ecx # was there a match in the last iter.? + cmovnz %rdi, %r8 # remember match if any + cmovnz %ecx, %esi + pxor %xmm2, %xmm2 + pcmpeqb %xmm1, %xmm2 # NUL byte present? + pcmpeqb %xmm0, %xmm1 # c present? + pmovmskb %xmm2, %eax + pmovmskb %xmm1, %ecx + lea 16(%rdi), %r9 + add $32, %rdi + test %eax, %eax # end of string in second half? + jz 0b + + ALIGN_TEXT +.Lend2: sub $16, %rdi +.Lend: lea -1(%rax), %edx + xor %edx, %eax # mask of bytes in the string + and %eax, %ecx # c found in the tail? + cmovnz %rdi, %r8 + cmovnz %ecx, %esi + bsr %esi, %esi # last location of c in (R8) + lea (%r8, %rsi, 1), %rax # pointer to match + ret +ARCHEND(strrchr, baseline) + .section .note.GNU-stack,"",%progbits
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