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The Datafile PD-CD 1 Issue 2
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PDCD-1 - Issue 02.iso
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_utilities
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utilities
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001
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src
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txtutils16
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lib
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c
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memcmp
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1993-05-01
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/* Copyright (C) 1991, 1993 Free Software Foundation, Inc.
Contributed by Torbjorn Granlund (tege@sics.se).
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#if defined (HAVE_STRING_H) || defined (_LIBC)
#include <string.h>
#endif
#ifdef _LIBC
#include <memcopy.h>
#else /* Not in the GNU C library. */
#include <sys/types.h>
/* Type to use for aligned memory operations.
This should normally be the biggest type supported by a single load
and store. */
#define op_t unsigned long int
#define OPSIZ (sizeof(op_t))
/* Threshold value for when to enter the unrolled loops. */
#define OP_T_THRES 16
/* Type to use for unaligned operations. */
typedef unsigned char byte;
#ifdef WORDS_BIGENDIAN
#define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
#else
#define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
#endif
#endif /* In the GNU C library. */
/* BE VERY CAREFUL IF YOU CHANGE THIS CODE! */
/* The strategy of this memcmp is:
1. Compare bytes until one of the block pointers is aligned.
2. Compare using memcmp_common_alignment or
memcmp_not_common_alignment, regarding the alignment of the other
block after the initial byte operations. The maximum number of
full words (of type op_t) are compared in this way.
3. Compare the few remaining bytes. */
/* memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t'
objects (not LEN bytes!). Both SRCP1 and SRCP2 should be aligned for
memory operations on `op_t's. */
#ifdef __GNUC__
__inline
#endif
static int
memcmp_common_alignment (srcp1, srcp2, len)
long int srcp1;
long int srcp2;
size_t len;
{
op_t a0, a1;
op_t b0, b1;
op_t res;
switch (len % 4)
{
case 2:
a0 = ((op_t *) srcp1)[0];
b0 = ((op_t *) srcp2)[0];
srcp1 -= 2 * OPSIZ;
srcp2 -= 2 * OPSIZ;
len += 2;
goto do1;
case 3:
a1 = ((op_t *) srcp1)[0];
b1 = ((op_t *) srcp2)[0];
srcp1 -= OPSIZ;
srcp2 -= OPSIZ;
len += 1;
goto do2;
case 0:
if (OP_T_THRES <= 3 * OPSIZ && len == 0)
return 0;
a0 = ((op_t *) srcp1)[0];
b0 = ((op_t *) srcp2)[0];
goto do3;
case 1:
a1 = ((op_t *) srcp1)[0];
b1 = ((op_t *) srcp2)[0];
srcp1 += OPSIZ;
srcp2 += OPSIZ;
len -= 1;
if (OP_T_THRES <= 3 * OPSIZ && len == 0)
goto do0;
/* Fall through. */
}
do
{
a0 = ((op_t *) srcp1)[0];
b0 = ((op_t *) srcp2)[0];
res = a1 - b1;
if (res != 0)
return res;
do3:
a1 = ((op_t *) srcp1)[1];
b1 = ((op_t *) srcp2)[1];
res = a0 - b0;
if (res != 0)
return res;
do2:
a0 = ((op_t *) srcp1)[2];
b0 = ((op_t *) srcp2)[2];
res = a1 - b1;
if (res != 0)
return res;
do1:
a1 = ((op_t *) srcp1)[3];
b1 = ((op_t *) srcp2)[3];
res = a0 - b0;
if (res != 0)
return res;
srcp1 += 4 * OPSIZ;
srcp2 += 4 * OPSIZ;
len -= 4;
}
while (len != 0);
/* This is the right position for do0. Please don't move
it into the loop. */
do0:
return a1 - b1;
}
/* SRCP2 should be aligned for memory operations on `op_t',
but SRCP1 *should be unaligned*. */
#ifdef __GNUC__
__inline
#endif
static int
memcmp_not_common_alignment (srcp1, srcp2, len)
long int srcp1;
long int srcp2;
size_t len;
{
op_t a0, a1, a2, a3;
op_t b0, b1, b2, b3;
op_t res;
op_t x;
int shl, shr;
/* Calculate how to shift a word read at the memory operation
aligned srcp1 to make it aligned for comparison. */
shl = 8 * (srcp1 % OPSIZ);
shr = 8 * OPSIZ - shl;
/* Make SRCP1 aligned by rounding it down to the beginning of the `op_t'
it points in the middle of. */
srcp1 &= -OPSIZ;
switch (len % 4)
{
case 2:
a1 = ((op_t *) srcp1)[0];
a2 = ((op_t *) srcp1)[1];
b2 = ((op_t *) srcp2)[0];
srcp1 -= 1 * OPSIZ;
srcp2 -= 2 * OPSIZ;
len += 2;
goto do1;
case 3:
a0 = ((op_t *) srcp1)[0];
a1 = ((op_t *) srcp1)[1];
b1 = ((op_t *) srcp2)[0];
srcp2 -= 1 * OPSIZ;
len += 1;
goto do2;
case 0:
if (OP_T_THRES <= 3 * OPSIZ && len == 0)
return 0;
a3 = ((op_t *) srcp1)[0];
a0 = ((op_t *) srcp1)[1];
b0 = ((op_t *) srcp2)[0];
srcp1 += 1 * OPSIZ;
goto do3;
case 1:
a2 = ((op_t *) srcp1)[0];
a3 = ((op_t *) srcp1)[1];
b3 = ((op_t *) srcp2)[0];
srcp1 += 2 * OPSIZ;
srcp2 += 1 * OPSIZ;
len -= 1;
if (OP_T_THRES <= 3 * OPSIZ && len == 0)
goto do0;
/* Fall through. */
}
do
{
a0 = ((op_t *) srcp1)[0];
b0 = ((op_t *) srcp2)[0];
x = MERGE(a2, shl, a3, shr);
res = x - b3;
if (res != 0)
return res;
do3:
a1 = ((op_t *) srcp1)[1];
b1 = ((op_t *) srcp2)[1];
x = MERGE(a3, shl, a0, shr);
res = x - b0;
if (res != 0)
return res;
do2:
a2 = ((op_t *) srcp1)[2];
b2 = ((op_t *) srcp2)[2];
x = MERGE(a0, shl, a1, shr);
res = x - b1;
if (res != 0)
return res;
do1:
a3 = ((op_t *) srcp1)[3];
b3 = ((op_t *) srcp2)[3];
x = MERGE(a1, shl, a2, shr);
res = x - b2;
if (res != 0)
return res;
srcp1 += 4 * OPSIZ;
srcp2 += 4 * OPSIZ;
len -= 4;
}
while (len != 0);
/* This is the right position for do0. Please don't move
it into the loop. */
do0:
x = MERGE(a2, shl, a3, shr);
return x - b3;
}
int
memcmp (s1, s2, len)
const void *s1;
const void *s2;
size_t len;
{
op_t a0;
op_t b0;
long int srcp1 = (long int) s1;
long int srcp2 = (long int) s2;
op_t res;
if (len >= OP_T_THRES)
{
/* There are at least some bytes to compare. No need to test
for LEN == 0 in this alignment loop. */
while (srcp2 % OPSIZ != 0)
{
a0 = ((byte *) srcp1)[0];
b0 = ((byte *) srcp2)[0];
srcp1 += 1;
srcp2 += 1;
res = a0 - b0;
if (res != 0)
return res;
len -= 1;
}
/* SRCP2 is now aligned for memory operations on `op_t'.
SRCP1 alignment determines if we can do a simple,
aligned compare or need to shuffle bits. */
if (srcp1 % OPSIZ == 0)
res = memcmp_common_alignment (srcp1, srcp2, len / OPSIZ);
else
res = memcmp_not_common_alignment (srcp1, srcp2, len / OPSIZ);
if (res != 0)
return res;
/* Number of bytes remaining in the interval [0..OPSIZ-1]. */
srcp1 += len & -OPSIZ;
srcp2 += len & -OPSIZ;
len %= OPSIZ;
}
/* There are just a few bytes to compare. Use byte memory operations. */
while (len != 0)
{
a0 = ((byte *) srcp1)[0];
b0 = ((byte *) srcp2)[0];
srcp1 += 1;
srcp2 += 1;
res = a0 - b0;
if (res != 0)
return res;
len -= 1;
}
return 0;
}