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tile: optimize memcmp
Customize memcmp.c for tile, using similar tricks from memcpy: - replace MERGE macro with dblalign. - replace memcmp_bytes function with revbytes. - use __glibc_likely. - use post-increment addressing. The schedule is still not perfect: the compiler is not hoisting code above the comparison branch, which could save a bundle or two. memcmp speeds up by 30-40% on shorter aligned tests in benchtest, with some tests with unaligned lengths taking a small performance hit.
This commit is contained in:
Chris Metcalf
parent
4b68ea1162
commit
d9cd52e64d
@ -1,5 +1,7 @@
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2014-10-02 Chris Metcalf <cmetcalf@tilera.com>
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* sysdeps/tile/memcmp.c: New file.
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* sysdeps/unix/sysv/linux/tile/sysconf.c: New file.
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* sysdeps/tile/tilegx/string-endian.h (STRSHIFT): New macro.
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367
sysdeps/tile/memcmp.c
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367
sysdeps/tile/memcmp.c
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@ -0,0 +1,367 @@
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/* Copyright (C) 1991-2014 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Torbjorn Granlund (tege@sics.se).
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifdef HAVE_CONFIG_H
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# include "config.h"
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#endif
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#undef __ptr_t
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#define __ptr_t void *
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#if defined HAVE_STRING_H || defined _LIBC
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# include <string.h>
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#endif
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#undef memcmp
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#ifndef MEMCMP
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# define MEMCMP memcmp
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#endif
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#ifdef _LIBC
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# include <memcopy.h>
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# include <endian.h>
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# if __BYTE_ORDER == __BIG_ENDIAN
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# define WORDS_BIGENDIAN
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# endif
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#else /* Not in the GNU C library. */
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# include <sys/types.h>
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/* Type to use for aligned memory operations.
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This should normally be the biggest type supported by a single load
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and store. Must be an unsigned type. */
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# define op_t unsigned long int
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# define OPSIZ (sizeof(op_t))
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/* Threshold value for when to enter the unrolled loops. */
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# define OP_T_THRES 16
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/* Type to use for unaligned operations. */
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typedef unsigned char byte;
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#endif /* In the GNU C library. */
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/* Provide the appropriate builtins to shift two registers based on
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the alignment of a pointer held in a third register, and to reverse
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the bytes in a word. */
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#ifdef __tilegx__
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#define DBLALIGN __insn_dblalign
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#define REVBYTES __insn_revbytes
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#else
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#define DBLALIGN __insn_dword_align
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#define REVBYTES __insn_bytex
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#endif
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#ifdef WORDS_BIGENDIAN
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# define CMP_LT_OR_GT(a, b) ((a) > (b) ? 1 : -1)
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#else
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# define CMP_LT_OR_GT(a, b) (REVBYTES(a) > REVBYTES(b) ? 1 : -1)
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#endif
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/* BE VERY CAREFUL IF YOU CHANGE THIS CODE! */
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/* The strategy of this memcmp is:
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1. Compare bytes until one of the block pointers is aligned.
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2. Compare using memcmp_common_alignment or
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memcmp_not_common_alignment, regarding the alignment of the other
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block after the initial byte operations. The maximum number of
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full words (of type op_t) are compared in this way.
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3. Compare the few remaining bytes. */
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static int memcmp_common_alignment (long, long, size_t) __THROW;
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/* memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t'
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objects (not LEN bytes!). Both SRCP1 and SRCP2 should be aligned for
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memory operations on `op_t's. */
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static int
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memcmp_common_alignment (srcp1, srcp2, len)
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long int srcp1;
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long int srcp2;
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size_t len;
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{
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op_t a0, a1;
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op_t b0, b1;
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switch (len % 4)
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{
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default: /* Avoid warning about uninitialized local variables. */
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case 2:
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a0 = ((op_t *) srcp1)[0];
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b0 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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len += 2;
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goto do1;
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case 3:
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a1 = ((op_t *) srcp1)[0];
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b1 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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len += 1;
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goto do2;
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case 0:
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if (OP_T_THRES <= 3 * OPSIZ && len == 0)
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return 0;
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a0 = ((op_t *) srcp1)[0];
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b0 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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goto do3;
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case 1:
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a1 = ((op_t *) srcp1)[0];
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b1 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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len -= 1;
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if (OP_T_THRES <= 3 * OPSIZ && len == 0)
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goto do0;
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/* Fall through. */
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}
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do
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{
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a0 = ((op_t *) srcp1)[0];
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b0 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (a1 != b1))
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return CMP_LT_OR_GT (a1, b1);
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do3:
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a1 = ((op_t *) srcp1)[0];
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b1 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (a0 != b0))
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return CMP_LT_OR_GT (a0, b0);
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do2:
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a0 = ((op_t *) srcp1)[0];
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b0 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (a1 != b1))
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return CMP_LT_OR_GT (a1, b1);
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do1:
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a1 = ((op_t *) srcp1)[0];
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b1 = ((op_t *) srcp2)[0];
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (a0 != b0))
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return CMP_LT_OR_GT (a0, b0);
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len -= 4;
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}
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while (len != 0);
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/* This is the right position for do0. Please don't move
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it into the loop. */
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do0:
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if (__glibc_likely (a1 != b1))
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return CMP_LT_OR_GT (a1, b1);
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return 0;
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}
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static int memcmp_not_common_alignment (long, long, size_t) __THROW;
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/* memcmp_not_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN
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`op_t' objects (not LEN bytes!). SRCP2 should be aligned for memory
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operations on `op_t', but SRCP1 *should be unaligned*. */
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static int
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memcmp_not_common_alignment (srcp1, srcp2, len)
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long int srcp1;
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long int srcp2;
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size_t len;
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{
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void * srcp1i;
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op_t a0, a1, a2, a3;
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op_t b0, b1, b2, b3;
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op_t x;
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/* Calculate how to shift a word read at the memory operation
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aligned srcp1 to make it aligned for comparison. */
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srcp1i = (void *) srcp1;
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/* Make SRCP1 aligned by rounding it down to the beginning of the `op_t'
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it points in the middle of. */
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srcp1 &= -OPSIZ;
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switch (len % 4)
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{
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default: /* Avoid warning about uninitialized local variables. */
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case 2:
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a1 = ((op_t *) srcp1)[0];
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a2 = ((op_t *) srcp1)[1];
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b2 = ((op_t *) srcp2)[0];
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srcp1 += 2 * OPSIZ;
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srcp2 += 1 * OPSIZ;
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len += 2;
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goto do1;
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case 3:
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a0 = ((op_t *) srcp1)[0];
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a1 = ((op_t *) srcp1)[1];
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b1 = ((op_t *) srcp2)[0];
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srcp1 += 2 * OPSIZ;
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srcp2 += 1 * OPSIZ;
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len += 1;
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goto do2;
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case 0:
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if (OP_T_THRES <= 3 * OPSIZ && len == 0)
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return 0;
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a3 = ((op_t *) srcp1)[0];
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a0 = ((op_t *) srcp1)[1];
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b0 = ((op_t *) srcp2)[0];
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srcp1 += 2 * OPSIZ;
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srcp2 += 1 * OPSIZ;
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goto do3;
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case 1:
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a2 = ((op_t *) srcp1)[0];
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a3 = ((op_t *) srcp1)[1];
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b3 = ((op_t *) srcp2)[0];
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srcp1 += 2 * OPSIZ;
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srcp2 += 1 * OPSIZ;
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len -= 1;
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if (OP_T_THRES <= 3 * OPSIZ && len == 0)
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goto do0;
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/* Fall through. */
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}
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do
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{
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a0 = ((op_t *) srcp1)[0];
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b0 = ((op_t *) srcp2)[0];
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x = DBLALIGN (a2, a3, srcp1i);
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (x != b3))
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return CMP_LT_OR_GT (x, b3);
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do3:
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a1 = ((op_t *) srcp1)[0];
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b1 = ((op_t *) srcp2)[0];
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x = DBLALIGN (a3, a0, srcp1i);
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (x != b0))
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return CMP_LT_OR_GT (x, b0);
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do2:
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a2 = ((op_t *) srcp1)[0];
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b2 = ((op_t *) srcp2)[0];
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x = DBLALIGN (a0, a1, srcp1i);
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (x != b1))
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return CMP_LT_OR_GT (x, b1);
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do1:
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a3 = ((op_t *) srcp1)[0];
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b3 = ((op_t *) srcp2)[0];
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x = DBLALIGN (a1, a2, srcp1i);
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srcp1 += OPSIZ;
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srcp2 += OPSIZ;
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if (__glibc_likely (x != b2))
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return CMP_LT_OR_GT (x, b2);
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len -= 4;
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}
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while (len != 0);
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/* This is the right position for do0. Please don't move
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it into the loop. */
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do0:
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x = DBLALIGN (a2, a3, srcp1i);
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if (__glibc_likely (x != b3))
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return CMP_LT_OR_GT (x, b3);
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return 0;
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}
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int
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MEMCMP (s1, s2, len)
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const __ptr_t s1;
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const __ptr_t s2;
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size_t len;
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{
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op_t a0;
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op_t b0;
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long int srcp1 = (long int) s1;
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long int srcp2 = (long int) s2;
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int res;
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if (len >= OP_T_THRES)
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{
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/* There are at least some bytes to compare. No need to test
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for LEN == 0 in this alignment loop. */
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while (srcp2 % OPSIZ != 0)
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{
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a0 = ((byte *) srcp1)[0];
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b0 = ((byte *) srcp2)[0];
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srcp1 += 1;
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srcp2 += 1;
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res = a0 - b0;
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if (__glibc_likely (res != 0))
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return res;
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len -= 1;
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}
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/* SRCP2 is now aligned for memory operations on `op_t'.
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SRCP1 alignment determines if we can do a simple,
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aligned compare or need to shuffle bits. */
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if (srcp1 % OPSIZ == 0)
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res = memcmp_common_alignment (srcp1, srcp2, len / OPSIZ);
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else
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res = memcmp_not_common_alignment (srcp1, srcp2, len / OPSIZ);
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if (res != 0)
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return res;
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/* Number of bytes remaining in the interval [0..OPSIZ-1]. */
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srcp1 += len & -OPSIZ;
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srcp2 += len & -OPSIZ;
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len %= OPSIZ;
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}
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/* There are just a few bytes to compare. Use byte memory operations. */
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while (len != 0)
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{
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a0 = ((byte *) srcp1)[0];
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b0 = ((byte *) srcp2)[0];
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srcp1 += 1;
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srcp2 += 1;
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res = a0 - b0;
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if (__glibc_likely (res != 0))
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return res;
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len -= 1;
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}
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return 0;
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}
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libc_hidden_builtin_def(memcmp)
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#ifdef weak_alias
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# undef bcmp
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weak_alias (memcmp, bcmp)
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#endif
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