Date: Sun, 30 Nov 2025 01:45:57 +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: 3f0dda7c5928 - stable/15 - libc: scalar strnlen() in RISC-V assembly Message-ID: <692ba1d5.2975f.6532a362@gitrepo.freebsd.org>
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The branch stable/15 has been updated by fuz: URL: https://cgit.FreeBSD.org/src/commit/?id=3f0dda7c59280fe05b57fe695022053cd8b7d5f1 commit 3f0dda7c59280fe05b57fe695022053cd8b7d5f1 Author: Strahinja Stanišić <strajabot@FreeBSD.org> AuthorDate: 2024-08-04 15:12:00 +0000 Commit: Robert Clausecker <fuz@FreeBSD.org> CommitDate: 2025-11-30 00:43:06 +0000 libc: scalar strnlen() in RISC-V assembly Optimized implementation of strnlen() in RISC-V assembly Performance was measured using strperf on a HiFive Unmatched (SiFive HF105-001) board. os: FreeBSD arch: riscv │ strnlen_baseline │ strnlen_scalar │ │ sec/op │ sec/op vs base │ Short 787.0µ ± 0% 430.9µ ± 1% -45.24% (p=0.000 n=20) Mid 621.6µ ± 0% 195.1µ ± 1% -68.61% (p=0.000 n=20) Long 569.4µ ± 1% 100.6µ ± 0% -82.34% (p=0.000 n=20) geomean 653.1µ 203.7µ -68.81% │ strnlen_baseline │ strnlen_scalar │ │ MiB/s │ MiB/s vs base │ Short 158.8 ± 0% 290.1 ± 1% +82.62% (p=0.000 n=20) Mid 201.1 ± 0% 640.6 ± 1% +218.59% (p=0.000 n=20) Long 219.5 ± 1% 1242.9 ± 0% +466.19% (p=0.000 n=20) geomean 191.4 613.5 +220.57% MFC after: 1 month MFC to: stable/15 Approved by: mhorne, markj (mentor) Reviewed by: fuz, Jari Sihvola <jsihv@gmx.com> Sponsored by: Google LLC (GSoC 2024) Differential Revision: https://reviews.freebsd.org/D46230 (cherry picked from commit 5a52f0704435b089199201be0029e0d7c9ef2fce) --- lib/libc/riscv/string/Makefile.inc | 1 + lib/libc/riscv/string/strnlen.S | 143 +++++++++++++++++++++++++++++++++++++ 2 files changed, 144 insertions(+) diff --git a/lib/libc/riscv/string/Makefile.inc b/lib/libc/riscv/string/Makefile.inc index ebea8d1d3412..4b97490a5494 100644 --- a/lib/libc/riscv/string/Makefile.inc +++ b/lib/libc/riscv/string/Makefile.inc @@ -3,4 +3,5 @@ MDSRCS+= \ memcpy.S \ memset.S \ strlen.S \ + strnlen.S \ strrchr.S diff --git a/lib/libc/riscv/string/strnlen.S b/lib/libc/riscv/string/strnlen.S new file mode 100644 index 000000000000..c0fd959548ff --- /dev/null +++ b/lib/libc/riscv/string/strnlen.S @@ -0,0 +1,143 @@ +/*- + * SPDX-License-Identifier: BSD-2-Clause + * + * Copyright (c) 2024 Strahinja Stanisic <strajabot@FreeBSD.org> + */ + +#include <machine/asm.h> + +/* + * a0 - const char *s + * a1 - size_t maxlen; + */ +ENTRY(strnlen) + /* + * a0 - const char *s; + * a1 - size_t maxlen; + * a2 - uint64_t *ptr; + * a3 - char iter[8]; + * a4 - uint64_t *end_align; + * a5 - uint64_t *end_unroll; + */ + + beqz a1, .Lnot_found + + /* ptr = s & ~0b111 */ + /* t0 = 0x0101010101010101 */ + /* t1 = 0x8080808080808080 */ + /* end_align = (s + maxlen + 7) & ~0b111 */ + /* mask_start = t0 >> ((-s.value) << 3) */ + add a4, a0, a1 + li t0, 0x01010101 + addi a4, a4, 7 + slli t1, t0, 32 + neg t2, a0 + andi a4, a4, ~0b111 + or t0, t0, t1 + slli t2, t2, 3 + andi a2, a0, ~0b111 + slli t1, t0, 7 + srl t2, t0, t2 + + /* if pointer is aligned skip to loop */ + beq a0, a2, .Lskip_start + + /* iter = *ptr */ + ld a3, (a2) + + /* iter = iter | mask_start */ + or a3, a3, t2 + + /* has_zero */ + not t2, a3 + sub a3, a3, t0 + and t2, t2, t1 + and a3, a3, t2 + + addi a2, a2, 8 + bnez a3, .Lfind_zero + +.Lskip_start: + /* end_unroll */ + sub t2, a4, a2 + andi t2, t2, ~0b1111 + add a5, a2, t2 + + /* while (ptr != end_unroll) */ + beq a2, a5, .Lskip_loop +.Lloop: + ld a3, (a2) + ld a6, 8(a2) + + /* has_zero */ + not t2, a3 + not t3, a6 + sub a3, a3, t0 + sub a6, a6, t0 + and t2, t2, t1 + and t3, t3, t1 + and a3, a3, t2 + and a6, a6, t3 + + addi a2, a2, 8 + bnez a3, .Lfind_zero + + mv a3, a6 + + addi a2, a2, 8 + bnez a3, .Lfind_zero + + bne a2, a5, .Lloop + +.Lskip_loop: + + beq a2, a4, .Lnot_found + + ld a3, (a2) + + /* has_zero */ + not t2, a3 + sub a3, a3, t0 + and t2, t2, t1 + and a3, a3, t2 + + + addi a2, a2, 8 + beqz a3, .Lnot_found + +.Lfind_zero: + + /* move ptr back */ + addi a2, a2, -8 + + /* isolate lowest set bit */ + neg t0, a3 + and a3, a3, t0 + + li t0, 0x0001020304050607 + srli a3, a3, 7 + + /* lowest set bit is 2^(8*k) + * multiplying by it shifts the idx array in t0 by k bytes to the left */ + mul a3, a3, t0 + + /* highest byte contains idx of first zero */ + srli a3, a3, 56 + + /* zero_idx */ + sub a2, a2, a0 + add a2, a2, a3 + + /* min(zero_idx, maxlen) */ + sub a2, a2, a1 + srai t1, a2, 63 + and a2, a2, t1 + add a0, a1, a2 + + ret + +.Lnot_found: + mv a0, a1 + ret + +END(strnlen)help
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