path: root/sysdeps/x86_64/multiarch/memcmp-sse2.S

/* memcmp with SSE2.
   Copyright (C) 2017-2025 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, see
   <https://www.gnu.org/licenses/>.  */


#include <isa-level.h>

/* MINIMUM_X86_ISA_LEVEL <= 2 because there is no V2 implementation
   so we need this to build for ISA V2 builds. */
#if ISA_SHOULD_BUILD (2)

#include <sysdep.h>

# ifndef MEMCMP
#  define MEMCMP __memcmp_sse2
# endif

# ifdef USE_AS_WMEMCMP
#  define PCMPEQ	pcmpeqd
#  define CHAR_SIZE	4
#  define SIZE_OFFSET	(0)
# else
#  define PCMPEQ	pcmpeqb
#  define CHAR_SIZE	1
# endif

# ifdef USE_AS_MEMCMPEQ
#  define SIZE_OFFSET	(0)
#  define CHECK_CMP(x, y)	subl x, y
# else
#  ifndef SIZE_OFFSET
#   define SIZE_OFFSET	(CHAR_PER_VEC * 2)
#  endif
#  define CHECK_CMP(x, y)	cmpl x, y
# endif

# define VEC_SIZE	16
# define CHAR_PER_VEC	(VEC_SIZE / CHAR_SIZE)

# ifndef MEMCMP
#  define MEMCMP	memcmp
# endif

	.text
ENTRY(MEMCMP)
#  ifdef __ILP32__
	/* Clear the upper 32 bits.  */
	movl	%edx, %edx
#  endif
# ifdef USE_AS_WMEMCMP
	/* Use 0xffff to test for mismatches on pmovmskb bitmask. Store
	   in ecx for code size. This is preferable to using `incw` as
	   it avoids partial register stalls on older hardware (pre
	   SnB).  */
	movl	$0xffff, %ecx
# endif
	cmpq	$CHAR_PER_VEC, %rdx
	ja	L(more_1x_vec)

# ifdef USE_AS_WMEMCMP
	/* saves a byte of code keeping the fall through path n = [2, 4]
	   in the initial cache line.  */
	decl	%edx
	jle	L(cmp_0_1)

	movq	(%rsi), %xmm0
	movq	(%rdi), %xmm1
	PCMPEQ	%xmm0, %xmm1
	pmovmskb %xmm1, %eax
	subl	%ecx, %eax
	jnz	L(ret_nonzero_vec_start_0)

	movq	-4(%rsi, %rdx, CHAR_SIZE), %xmm0
	movq	-4(%rdi, %rdx, CHAR_SIZE), %xmm1
	PCMPEQ	%xmm0, %xmm1
	pmovmskb %xmm1, %eax
	subl	%ecx, %eax
	jnz	L(ret_nonzero_vec_end_0_adj)
# else
	cmpl	$8, %edx
	ja	L(cmp_9_16)

	cmpl	$4, %edx
	jb	L(cmp_0_3)

#  ifdef USE_AS_MEMCMPEQ
	movl	(%rsi), %eax
	subl	(%rdi), %eax

	movl	-4(%rsi, %rdx), %esi
	subl	-4(%rdi, %rdx), %esi

	orl	%esi, %eax
	ret
#  else
	/* Combine comparisons for lo and hi 4-byte comparisons.  */
	movl	-4(%rsi, %rdx), %ecx
	movl	-4(%rdi, %rdx), <