/* Searching in a string.
- Copyright (C) 2008-2021 Free Software Foundation, Inc.
+ Copyright (C) 2008-2022 Free Software Foundation, Inc.
- This program is free software: you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 3 of the License, or
- (at your option) any later version.
+ This file 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.
- This program is distributed in the hope that it will be useful,
+ This file 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 General Public License for more details.
+ GNU Lesser General Public License for more details.
- You should have received a copy of the GNU General Public License
+ You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include <string.h>
+/* A function definition is only needed if HAVE_RAWMEMCHR is not defined. */
+#if !HAVE_RAWMEMCHR
+
+# include <limits.h>
+# include <stdalign.h>
+# include <stdint.h>
+
+# include "verify.h"
+
/* Find the first occurrence of C in S. */
void *
rawmemchr (const void *s, int c_in)
{
- /* On 32-bit hardware, choosing longword to be a 32-bit unsigned
- long instead of a 64-bit uintmax_t tends to give better
- performance. On 64-bit hardware, unsigned long is generally 64
- bits already. Change this typedef to experiment with
- performance. */
- typedef unsigned long int longword;
+ /* Change this typedef to experiment with performance. */
+ typedef uintptr_t longword;
+ /* If you change the "uintptr_t", you should change UINTPTR_WIDTH to match.
+ This verifies that the type does not have padding bits. */
+ verify (UINTPTR_WIDTH == UCHAR_WIDTH * sizeof (longword));
const unsigned char *char_ptr;
- const longword *longword_ptr;
- longword repeated_one;
- longword repeated_c;
- unsigned char c;
-
- c = (unsigned char) c_in;
+ unsigned char c = c_in;
/* Handle the first few bytes by reading one byte at a time.
Do this until CHAR_PTR is aligned on a longword boundary. */
for (char_ptr = (const unsigned char *) s;
- (size_t) char_ptr % sizeof (longword) != 0;
+ (uintptr_t) char_ptr % alignof (longword) != 0;
++char_ptr)
if (*char_ptr == c)
return (void *) char_ptr;
- longword_ptr = (const longword *) char_ptr;
-
- /* All these elucidatory comments refer to 4-byte longwords,
- but the theory applies equally well to any size longwords. */
+ longword const *longword_ptr = s = char_ptr;
/* Compute auxiliary longword values:
repeated_one is a value which has a 1 in every byte.
repeated_c has c in every byte. */
- repeated_one = 0x01010101;
- repeated_c = c | (c << 8);
- repeated_c |= repeated_c << 16;
- if (0xffffffffU < (longword) -1)
- {
- repeated_one |= repeated_one << 31 << 1;
- repeated_c |= repeated_c << 31 << 1;
- if (8 < sizeof (longword))
- {
- size_t i;
-
- for (i = 64; i < sizeof (longword) * 8; i *= 2)
- {
- repeated_one |= repeated_one << i;
- repeated_c |= repeated_c << i;
- }
- }
- }
+ longword repeated_one = (longword) -1 / UCHAR_MAX;
+ longword repeated_c = repeated_one * c;
+ longword repeated_hibit = repeated_one * (UCHAR_MAX / 2 + 1);
/* Instead of the traditional loop which tests each byte, we will
- test a longword at a time. The tricky part is testing if *any of
- the four* bytes in the longword in question are equal to NUL or
+ test a longword at a time. The tricky part is testing if any of
+ the bytes in the longword in question are equal to
c. We first use an xor with repeated_c. This reduces the task
- to testing whether *any of the four* bytes in longword1 is zero.
+ to testing whether any of the bytes in longword1 is zero.
+
+ (The following comments assume 8-bit bytes, as POSIX requires;
+ the code's use of UCHAR_MAX should work even if bytes have more
+ than 8 bits.)
We compute tmp =
- ((longword1 - repeated_one) & ~longword1) & (repeated_one << 7).
+ ((longword1 - repeated_one) & ~longword1) & (repeated_one * 0x80).
That is, we perform the following operations:
1. Subtract repeated_one.
2. & ~longword1.
{
longword longword1 = *longword_ptr ^ repeated_c;
- if ((((longword1 - repeated_one) & ~longword1)
- & (repeated_one << 7)) != 0)
+ if ((((longword1 - repeated_one) & ~longword1) & repeated_hibit) != 0)
break;
longword_ptr++;
}
- char_ptr = (const unsigned char *) longword_ptr;
+ char_ptr = s = longword_ptr;
/* At this point, we know that one of the sizeof (longword) bytes
- starting at char_ptr is == c. On little-endian machines, we
+ starting at char_ptr is == c. If we knew endianness, we
could determine the first such byte without any further memory
accesses, just by looking at the tmp result from the last loop
- iteration. But this does not work on big-endian machines.
- Choose code that works in both cases. */
+ iteration. However, the following simple and portable code does
+ not attempt this potential optimization. */
- char_ptr = (unsigned char *) longword_ptr;
while (*char_ptr != c)
char_ptr++;
return (void *) char_ptr;
}
+
+#endif
projects / thirdparty / binutils-gdb.git / blobdiff