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lib/libc/string: replace ffs/fls implementations with clang builtins

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Most architectures we support (except for riscv64) have instructions
to compute these functions very quickly.  Replace old code with the
ffs and clz builtin functions, allowing clang to generate good code
for all architectures.

As a consequence, toss out arm and i386 ffs() implementations.

Sponsored by:	FreeBSD Foundation
Approved by:	mhorne
MFC after:	1 week
Differential Revision: https://reviews.freebsd.org/D40730
This commit is contained in:
Robert Clausecker 2023-06-23 18:22:54 +02:00
parent 49390697b9
commit ee8b0c436d
10 changed files with 34 additions and 157 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
lib/libc/arm/string/Makefile.inc
View file

@ -3,7 +3,6 @@
MDSRCS+= \
bcopy.S \
bzero.S \
ffs.S \
memcmp.S \
memcpy.S \
memmove.S \

57
lib/libc/arm/string/ffs.S
View file

@ -1,57 +0,0 @@
/* $NetBSD: ffs.S,v 1.5 2003/04/05 23:08:52 bjh21 Exp $ */
/*
* Copyright (c) 2001 Christopher Gilbert
* All rights reserved.
*
* 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. The name of the company nor the name of the author may be used to
* endorse or promote products derived from this software without specific
* prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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>
__FBSDID("$FreeBSD$");
.syntax unified
/*
* ffs - find first set bit, this algorithm isolates the first set
* bit, then multiplies the number by 0x0450fbaf which leaves the top
* 6 bits as an index into the table. This algorithm should be a win
* over the checking each bit in turn as per the C compiled version.
*
* This is the ffs algorithm devised by d.seal and posted to comp.sys.arm on
* 16 Feb 1994.
*/
ENTRY(ffs)
/* Standard trick to isolate bottom bit in r0 or 0 if r0 = 0 on entry */
rsb r1, r0, #0
ands r0, r0, r1
itt ne
clzne r0, r0
rsbne r0, r0, #32
RET
END(ffs)
.section .note.GNU-stack,"",%progbits

1
lib/libc/i386/string/Makefile.inc
View file

@ -4,7 +4,6 @@ MDSRCS+= \
bcmp.S \
bcopy.S \
bzero.S \
ffs.S \
memcmp.S \
memcpy.S \
memmove.S \

56
lib/libc/i386/string/ffs.S
View file

@ -1,56 +0,0 @@
/*
* Copyright (c) 1993 Winning Strategies, Inc.
* All rights reserved.
*
* 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. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by Winning Strategies, Inc.
* 4. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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>
__FBSDID("$FreeBSD$");
/*
* ffs(value)
* finds the first bit set in value and returns the index of
* that bit. Bits are numbered starting from 1, starting at the
* rightmost bit. A return value of 0 means that the argument
* was zero.
*
* Written by:
* J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
*/
ENTRY(ffs)
bsfl 4(%esp),%eax
jz L1 /* ZF is set if all bits are 0 */
incl %eax /* bits numbered from 1, not 0 */
ret
.align 2
L1: xorl %eax,%eax /* clear result */
ret
END(ffs)
.section .note.GNU-stack,"",%progbits

12
lib/libc/string/ffs.c
View file

@ -3,6 +3,10 @@
*
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2023 The FreeBSD Foundation
*
* Portions of this software were 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
@ -43,11 +47,5 @@ __FBSDID("$FreeBSD$");
int
ffs(int mask)
{
int bit;
if (mask == 0)
return(0);
for (bit = 1; !(mask & 1); bit++)
mask = (unsigned int)mask >> 1;
return (bit);
return (__builtin_ffs(mask));
}

12
lib/libc/string/ffsl.c
View file

@ -3,6 +3,10 @@
*
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2023 The FreeBSD Foundation
*
* Portions of this software were 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
@ -40,11 +44,5 @@ __FBSDID("$FreeBSD$");
int
ffsl(long mask)
{
int bit;
if (mask == 0)
return (0);
for (bit = 1; !(mask & 1); bit++)
mask = (unsigned long)mask >> 1;
return (bit);
return (__builtin_ffsl(mask));
}

12
lib/libc/string/ffsll.c
View file

@ -3,6 +3,10 @@
*
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2023 The FreeBSD Foundation
*
* Portions of this software were 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
@ -40,11 +44,5 @@ __FBSDID("$FreeBSD$");
int
ffsll(long long mask)
{
int bit;
if (mask == 0)
return (0);
for (bit = 1; !(mask & 1); bit++)
mask = (unsigned long long)mask >> 1;
return (bit);
return (__builtin_ffsll(mask));
}

13
lib/libc/string/fls.c
View file

@ -3,6 +3,10 @@
*
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2023 The FreeBSD Foundation
*
* Portions of this software were 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
@ -32,6 +36,7 @@
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <limits.h>
#include <strings.h>
/*
@ -40,11 +45,5 @@ __FBSDID("$FreeBSD$");
int
fls(int mask)
{
int bit;
if (mask == 0)
return (0);
for (bit = 1; mask != 1; bit++)
mask = (unsigned int)mask >> 1;
return (bit);
return (mask == 0 ? 0 : CHAR_BIT * sizeof(mask) - __builtin_clz(mask));
}

14
lib/libc/string/flsl.c
View file

@ -3,6 +3,11 @@
*
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2023 The FreeBSD Foundation
*
* Portions of this software were 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
@ -32,6 +37,7 @@
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <limits.h>
#include <strings.h>
/*
@ -40,11 +46,5 @@ __FBSDID("$FreeBSD$");
int
flsl(long mask)
{
int bit;
if (mask == 0)
return (0);
for (bit = 1; mask != 1; bit++)
mask = (unsigned long)mask >> 1;
return (bit);
return (mask == 0 ? 0 : CHAR_BIT * sizeof(mask) - __builtin_clzl(mask));
}

13
lib/libc/string/flsll.c
View file

@ -3,6 +3,10 @@
*
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2023 The FreeBSD Foundation
*
* Portions of this software were 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
@ -32,6 +36,7 @@
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <limits.h>
#include <strings.h>
/*
@ -40,11 +45,5 @@ __FBSDID("$FreeBSD$");
int
flsll(long long mask)
{
int bit;
if (mask == 0)
return (0);
for (bit = 1; mask != 1; bit++)
mask = (unsigned long long)mask >> 1;
return (bit);
return (mask == 0 ? 0 : CHAR_BIT * sizeof(mask) - __builtin_clzll(mask));
}