From bac2eea13ae3e4dc8fd2aec261b2a18930138495 Mon Sep 17 00:00:00 2001 From: rilysh Date: Mon, 22 Apr 2024 15:52:25 -0600 Subject: [PATCH] swab.c(libc): use a simplified version of byte swapping This version of swab function simplifies the logic of swapping adjacent bytes. Previous version of swab() used an arbitrary unrolling, which was relevant back in the day but unnecessary for modern compilers, as if the input size is known at compile time, they can do it automatically. This version of swab() is inspired by musl. A similar version can be found at: https://github.com/openbsd/src/blob/master/lib/libc/string/swab.c Signed-off-by: rilysh Reviewed by: imp Pull Request: https://github.com/freebsd/freebsd-src/pull/1086 --- lib/libc/string/swab.c | 58 ++++++++---------------------------------- 1 file changed, 11 insertions(+), 47 deletions(-) diff --git a/lib/libc/string/swab.c b/lib/libc/string/swab.c index e3765fa08d07..2b044d68ca46 100644 --- a/lib/libc/string/swab.c +++ b/lib/libc/string/swab.c @@ -1,35 +1,6 @@ /*- - * SPDX-License-Identifier: BSD-3-Clause - * - * Copyright (c) 1988, 1993 - * The Regents of the University of California. All rights reserved. - * - * This code is derived from software contributed to Berkeley by - * Jeffrey Mogul. - * - * 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. - * 3. Neither the name of the University nor the names of its contributors - * may be used to endorse or promote products derived from this software - * without specific prior written permission. - * - * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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. + * SPDX-License-Identifier: BSD-2-Clause + * Copyright (c) 2024 rilysh */ #include @@ -37,22 +8,15 @@ void swab(const void * __restrict from, void * __restrict to, ssize_t len) { - unsigned char temp; - size_t n; - const unsigned char *fp; - unsigned char *tp; + const unsigned char *f = from; + unsigned char *t = to; - if (len <= 0) - return; - n = (size_t)len >> 1; - fp = (const unsigned char *)from; - tp = (unsigned char *)to; -#define STEP temp = *fp++,*tp++ = *fp++,*tp++ = temp - /* round to multiple of 8 */ - for (; n & 0x7; --n) - STEP; - for (n >>= 3; n > 0; --n) { - STEP; STEP; STEP; STEP; - STEP; STEP; STEP; STEP; + while (len > 1) { + t[0] = f[1]; + t[1] = f[0]; + + f += 2; + t += 2; + len -= 2; } }