[thirdparty/glibc.git] / sysdeps / i386 / memcmp.S

/* Compare two memory blocks for differences in the first COUNT bytes.
   Copyright (C) 1995, 1996, 1997, 2000, 2004 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <sysdep.h>
#include "asm-syntax.h"
#include "bp-sym.h"
#include "bp-asm.h"

#define PARMS	LINKAGE+4	/* space for 1 saved reg */
#define BLK1	PARMS
#define BLK2	BLK1+PTR_SIZE
#define LEN	BLK2+PTR_SIZE

	.text
ENTRY (BP_SYM (memcmp))
	ENTER

	pushl %esi		/* Save callee-safe registers.  */
	movl %edi, %edx		/* Note that %edx is not used and can
				   so be used to save %edi.  It's faster.  */

	movl BLK1(%esp), %esi
	movl BLK2(%esp), %edi
	movl LEN(%esp), %ecx
	CHECK_BOUNDS_LOW (%esi, BLK1(%esp))
	CHECK_BOUNDS_LOW (%edi, BLK2(%esp))

	cld			/* Set direction of comparison.  */

	xorl %eax, %eax		/* Default result.  */

	repe			/* Compare at most %ecx bytes.  */
	cmpsb
	jz L(1)			/* If even last byte was equal we return 0.  */

	/* The memory blocks are not equal.  So result of the last
	   subtraction is present in the carry flag.  It is set when
	   the byte in block #2 is bigger.  In this case we have to
	   return -1 (=0xffffffff), else 1.  */
	sbbl %eax, %eax		/* This is tricky.  %eax == 0 and carry is set
				   or not depending on last subtraction.  */

	/* At this point %eax == 0, if the byte of block #1 was bigger, and
	   0xffffffff if the last byte of block #2 was bigger.  The latter
	   case is already correct but the former needs a little adjustment.
	   Note that the following operation does not change 0xffffffff.  */
	orb $1, %al		/* Change 0 to 1.  */

L(1):	CHECK_BOUNDS_HIGH (%esi, BLK1(%esp), jbe)
	CHECK_BOUNDS_HIGH (%edi, BLK2(%esp), jbe)
	popl %esi		/* Restore registers.  */
	movl %edx, %edi

	LEAVE
	ret
END (BP_SYM (memcmp))

#undef bcmp
weak_alias (BP_SYM (memcmp), BP_SYM (bcmp))
libc_hidden_builtin_def (BP_SYM (memcmp))
Commit	Line	Data
5929563f	1	/* Compare two memory blocks for differences in the first COUNT bytes.
a334319f	2	Copyright (C) 1995, 1996, 1997, 2000, 2004 Free Software Foundation, Inc.
5929563f	3	This file is part of the GNU C Library.
8f5ca04b	4
5929563f	5	The GNU C Library is free software; you can redistribute it and/or
41bdb6e2 AJ	6	modify it under the terms of the GNU Lesser General Public
	7	License as published by the Free Software Foundation; either
	8	version 2.1 of the License, or (at your option) any later version.
8f5ca04b	9
5929563f UD	10	The GNU C Library is distributed in the hope that it will be useful,
	11	but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
41bdb6e2	13	Lesser General Public License for more details.
8f5ca04b	14
41bdb6e2 AJ	15	You should have received a copy of the GNU Lesser General Public
	16	License along with the GNU C Library; if not, write to the Free
	17	Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
	18	02111-1307 USA. */
8f5ca04b RM	19
	20	#include <sysdep.h>
	21	#include "asm-syntax.h"
2fc08826	22	#include "bp-sym.h"
3f02f778	23	#include "bp-asm.h"
8f5ca04b	24
3f02f778 GM	25	#define PARMS LINKAGE+4 /* space for 1 saved reg */
	26	#define BLK1 PARMS
	27	#define BLK2 BLK1+PTR_SIZE
	28	#define LEN BLK2+PTR_SIZE
8f5ca04b RM	29
8f5ca04b RM	30	.text
2fc08826	31	ENTRY (BP_SYM (memcmp))
3f02f778 GM	32	ENTER
3f02f778 GM	33
8f5ca04b RM	34	pushl %esi /* Save callee-safe registers. */
	35	movl %edi, %edx /* Note that %edx is not used and can
	36	so be used to save %edi. It's faster. */
	37
3f02f778 GM	38	movl BLK1(%esp), %esi
	39	movl BLK2(%esp), %edi
	40	movl LEN(%esp), %ecx
53c06508 GM	41	CHECK_BOUNDS_LOW (%esi, BLK1(%esp))
53c06508 GM	42	CHECK_BOUNDS_LOW (%edi, BLK2(%esp))
8f5ca04b RM	43
	44	cld /* Set direction of comparison. */
	45
	46	xorl %eax, %eax /* Default result. */
	47
	48	repe /* Compare at most %ecx bytes. */
	49	cmpsb
5929563f	50	jz L(1) /* If even last byte was equal we return 0. */
8f5ca04b RM	51
	52	/* The memory blocks are not equal. So result of the last
	53	subtraction is present in the carry flag. It is set when
	54	the byte in block #2 is bigger. In this case we have to
	55	return -1 (=0xffffffff), else 1. */
	56	sbbl %eax, %eax /* This is tricky. %eax == 0 and carry is set
	57	or not depending on last subtraction. */
	58
	59	/* At this point %eax == 0, if the byte of block #1 was bigger, and
49c091e5	60	0xffffffff if the last byte of block #2 was bigger. The latter
8f5ca04b RM	61	case is already correct but the former needs a little adjustment.
	62	Note that the following operation does not change 0xffffffff. */
	63	orb $1, %al /* Change 0 to 1. */
	64
53c06508 GM	65	L(1): CHECK_BOUNDS_HIGH (%esi, BLK1(%esp), jbe)
	66	CHECK_BOUNDS_HIGH (%edi, BLK2(%esp), jbe)
	67	popl %esi /* Restore registers. */
8f5ca04b RM	68	movl %edx, %edi
8f5ca04b RM	69
3f02f778	70	LEAVE
8f5ca04b	71	ret
2fc08826	72	END (BP_SYM (memcmp))
8f5ca04b RM	73
8f5ca04b RM	74	#undef bcmp
2fc08826	75	weak_alias (BP_SYM (memcmp), BP_SYM (bcmp))
758b2153	76	libc_hidden_builtin_def (BP_SYM (memcmp))