lib/libutils/isoc/newlib/memchr.c

// SPDX-License-Identifier: BSD-3-Clause
/*
 * Copyright (c) 1994-2009  Red Hat, Inc.
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * 3. Neither the name of the copyright holder nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 */

/*
FUNCTION
	<<memchr>>---find character in memory

INDEX
	memchr

ANSI_SYNOPSIS
	#include <string.h>
	void *memchr(const void *<[src]>, int <[c]>, size_t <[length]>);

TRAD_SYNOPSIS
	#include <string.h>
	void *memchr(<[src]>, <[c]>, <[length]>)
	void *<[src]>;
	void *<[c]>;
	size_t <[length]>;

DESCRIPTION
	This function searches memory starting at <<*<[src]>>> for the
	character <[c]>.  The search only ends with the first
	occurrence of <[c]>, or after <[length]> characters; in
	particular, <<NUL>> does not terminate the search.

RETURNS
	If the character <[c]> is found within <[length]> characters
	of <<*<[src]>>>, a pointer to the character is returned. If
	<[c]> is not found, then <<NULL>> is returned.

PORTABILITY
<<memchr>> is ANSI C.

<<memchr>> requires no supporting OS subroutines.

QUICKREF
	memchr ansi pure
*/

#include "_ansi.h"
#include <string.h>
#include <limits.h>

/* Nonzero if either X or Y is not aligned on a "long" boundary.  */
#define UNALIGNED(X) ((long)X & (sizeof(long) - 1))

/* How many bytes are loaded each iteration of the word copy loop.  */
#define LBLOCKSIZE (sizeof(long))

/* Threshhold for punting to the bytewise iterator.  */
#define TOO_SMALL(LEN)  ((LEN) < LBLOCKSIZE)

#if LONG_MAX == 2147483647L
#define DETECTNULL(X) (((X) - 0x01010101L) & ~(X) & 0x80808080UL)
#else
#if LONG_MAX == 9223372036854775807L
/* Nonzero if X (a long int) contains a NULL byte. */
#define DETECTNULL(X) (((X) - 0x0101010101010101L) & ~(X) & \
		       0x8080808080808080UL)
#else
#error long int is not a 32bit or 64bit type.
#endif
#endif

#ifndef DETECTNULL
#error long int is not a 32bit or 64bit byte
#endif

/* DETECTCHAR returns nonzero if (long)X contains the byte used
   to fill (long)MASK. */
#define DETECTCHAR(X, MASK) (DETECTNULL(X ^ MASK))

_PTR
_DEFUN(memchr, (src_void, c, length), _CONST _PTR src_void _AND int c
	_AND size_t length)
{
	_CONST unsigned char *src = (_CONST unsigned char *)src_void;
	unsigned char d = c;

#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
	unsigned long *asrc;
	unsigned long mask;
	int i;

	while (UNALIGNED(src)) {
		if (!length--)
			return NULL;
		if (*src == d)
			return (void *)src;
		src++;
	}

	if (!TOO_SMALL(length)) {
		/* If we get this far, we know that length is large and src is
		   word-aligned. */
		/* The fast code reads the source one word at a time and only
		   performs the bytewise search on word-sized segments if they
		   contain the search character, which is detected by XORing
		   the word-sized segment with a word-sized block of the search
		   character and then detecting for the presence of NUL in the
		   result.  */
		asrc = (unsigned long *)src;
		mask = d << 8 | d;
		mask = mask << 16 | mask;
		for (i = 32; i < LBLOCKSIZE * 8; i <<= 1)
			mask = (mask << i) | mask;

		while (length >= LBLOCKSIZE) {
			if (DETECTCHAR(*asrc, mask))
				break;
			length -= LBLOCKSIZE;
			asrc++;
		}

		/* If there are fewer than LBLOCKSIZE characters left,
		   then we resort to the bytewise loop.  */

		src = (unsigned char *)asrc;
	}
#endif /* not PREFER_SIZE_OVER_SPEED */

	while (length--) {
		if (*src == d)
			return (void *)src;
		src++;
	}

	return NULL;
}