Date: Sun, 30 Nov 2025 01:45:59 +0000 From: Robert Clausecker <fuz@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Cc: Strahinja =?utf-8?Q?Stani=C5=A1?==?utf-8?Q?i=C4=87?= <strajabot@FreeBSD.org> Subject: git: f56c68448d42 - stable/15 - libc: scalar strchrnul() in RISC-V assembly Message-ID: <692ba1d7.28665.9efa142@gitrepo.freebsd.org>
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The branch stable/15 has been updated by fuz: URL: https://cgit.FreeBSD.org/src/commit/?id=f56c68448d429687a81ce4d97b16e7b9d7c57808 commit f56c68448d429687a81ce4d97b16e7b9d7c57808 Author: Strahinja Stanišić <strajabot@FreeBSD.org> AuthorDate: 2024-07-19 17:58:04 +0000 Commit: Robert Clausecker <fuz@FreeBSD.org> CommitDate: 2025-11-30 00:43:06 +0000 libc: scalar strchrnul() in RISC-V assembly Scalar implementation of strchrnul() in RISC-V assembly and changes to the corresponding manpage. Performance was benchmarked on a HiFive Unmatched (SiFive HF105-001) board using: https://github.com/clausecker/strperf os: FreeBSD arch: riscv │ strchrnul_baseline │ strchrnul_scalar │ │ sec/op │ sec/op vs base │ Short 680.2µ ± 5% 435.3µ ± 0% -36.01% (p=0.000 n=20) Mid 314.7µ ± 3% 221.4µ ± 0% -29.63% (p=0.000 n=20) Long 152.3µ ± 0% 138.5µ ± 0% -9.08% (p=0.000 n=20) geomean 319.5µ 237.2µ -25.75% │ strchrnul_baseline │ strchrnul_scalar │ │ MiB/s │ MiB/s vs base │ Short 183.8 ± 5% 287.2 ± 0% +56.27% (p=0.000 n=20) Mid 397.3 ± 3% 564.6 ± 0% +42.12% (p=0.000 n=20) Long 820.5 ± 0% 902.5 ± 0% +9.99% (p=0.000 n=20) geomean 391.3 527.0 +34.68% MFC after: 1 month MFC to: stable/15 Approved by: markj (mentor) Reviewed by: fuz Sponsored by: Google LLC (GSoC 2024) Differential Revision: https://reviews.freebsd.org/D46047 (cherry picked from commit 08af0bbc9c7d71bbaadb31ad31f8492f40537c5c) --- lib/libc/riscv/string/Makefile.inc | 1 + lib/libc/riscv/string/strchrnul.S | 116 +++++++++++++++++++++++++++++++++++++ 2 files changed, 117 insertions(+) diff --git a/lib/libc/riscv/string/Makefile.inc b/lib/libc/riscv/string/Makefile.inc index 4b97490a5494..719f22f6077f 100644 --- a/lib/libc/riscv/string/Makefile.inc +++ b/lib/libc/riscv/string/Makefile.inc @@ -4,4 +4,5 @@ MDSRCS+= \ memset.S \ strlen.S \ strnlen.S \ + strchrnul.S \ strrchr.S diff --git a/lib/libc/riscv/string/strchrnul.S b/lib/libc/riscv/string/strchrnul.S new file mode 100644 index 000000000000..8abba71c4199 --- /dev/null +++ b/lib/libc/riscv/string/strchrnul.S @@ -0,0 +1,116 @@ +/*- + * SPDX-License-Identifier: BSD-2-Clause + * + * Copyright (c) 2024 Strahinja Stanisic <strajabot@FreeBSD.org> + */ + +#include <machine/asm.h> + + .weak strchrnul + .set strchrnul, __strchrnul + +/* + * a0 - const char *str + * a1 - int c; + */ +ENTRY(__strchrnul) + /* + * a0 - const char *ptr; + * a1 - char cccccccc[8]; + * a2 - char iter[8]; + * a3 - char mask_end + */ + + /* int to char */ + andi a1, a1, 0xFF + + /* t0 = 0x0101010101010101 */ + li t0, 0x01010101 + slli t1, t0, 32 + or t0, t0, t1 + + /* t1 = 0x8080808080808080 */ + slli t1, t0, 7 + + /* spread char across bytes */ + mul a1, a1, t0 + + /* align_offset */ + andi t2, a0, 0b111 + + /* align pointer */ + andi a0, a0, ~0b111 + + /* if pointer is aligned skip to loop */ + beqz t2, .Lloop + + ld a2, (a0) + + /* mask_start calculation */ + slli t2, t2, 3 + neg t2, t2 + srl t2, t0, t2 + + /* fill bytes before start with non-zero */ + or a3, a2, t2 + + xor a2, a2, a1 + or a2, a2, t2 + + /* has_zero for \0 */ + not t3, a3 + not t2, a2 + sub a3, a3, t0 + sub a2, a2, t0 + and a3, a3, t3 + and a2, a2, t2 + and a3, a3, t1 + and a2, a2, t1 + + + /* if \0 or c was found, exit */ + or a2, a2, a3 + addi a0, a0, 8 + bnez a2, .Lfind_char + + +.Lloop: + ld a2, (a0) + + /* has_zero for both \0 or c */ + xor a3, a2, a1 + + not t2, a2 + not t3, a3 + sub a2, a2, t0 + sub a3, a3, t0 + and a2, a2, t2 + and a3, a3, t3 + and a2, a2, t1 + and a3, a3, t1 + + /* if \0 or c was found, exit */ + or a2, a2, a3 + addi a0, a0, 8 + beqz a2, .Lloop + +.Lfind_char: + addi a0, a0, -8 + + /* isolate lowest set bit */ + neg t0, a2 + and a2, a2, t0 + + li t0, 0x0001020304050607 + srli a2, a2, 7 + + /* lowest set bit is 2^(8*k) + * multiplying by it shifts the idx array in t0 by k bytes to the left */ + mul a2, a2, t0 + + /* highest byte contains idx of first zero */ + srli a2, a2, 56 + + add a0, a0, a2 + ret +END(__strchrnul)help
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