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https://github.com/apache/nuttx.git
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anjiahao
7c96537a58
This allows the compiler to automatically identify which string functions can be compiled into libraries, and the compiler's internal implementation is faster than libc functions. Signed-off-by: anjiahao <anjiahao@xiaomi.com>
163 lines
4.2 KiB
C
163 lines
4.2 KiB
C
/****************************************************************************
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* libs/libc/string/lib_bsdstrchr.c
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*
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* Copyright (c) 1994-2009 Red Hat, Inc. All rights reserved.
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*
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* This copyrighted material is made available to anyone wishing to use,
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* modify, copy, or redistribute it subject to the terms and conditions
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* of the BSD License. This program is distributed in the hope that
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* it will be useful, but WITHOUT ANY WARRANTY expressed or implied,
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* including the implied warranties of MERCHANTABILITY or FITNESS FOR
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* A PARTICULAR PURPOSE. A copy of this license is available at
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* http://www.opensource.org/licenses. Any Red Hat trademarks that are
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* incorporated in the source code or documentation are not subject to
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* the BSD License and may only be used or replicated with the express
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* permission of Red Hat, Inc.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <string.h>
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#include "libc.h"
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define UNALIGNED(x) ((long)(uintptr_t)(x) & (sizeof(long) - 1))
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/* How many bytes are loaded each iteration of the word copy loop. */
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#define LBLOCKSIZE (sizeof(long))
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/* Macros for detecting endchar */
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#if LONG_MAX == 2147483647
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# define DETECTNULL(x) (((x) - 0x01010101) & ~(x) & 0x80808080)
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#elif LONG_MAX == 9223372036854775807
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/* Nonzero if x (a long int) contains a NULL byte. */
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# define DETECTNULL(x) (((x) - 0x0101010101010101) & ~(x) & 0x8080808080808080)
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#endif
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#define DETECTCHAR(x, mask) (DETECTNULL((x) ^ (mask)))
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: strchr
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*
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* Description:
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* The strchr() function locates the first occurrence of 'c' (converted to
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* a char) in the string pointed to by 's'. The terminating null byte is
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* considered to be part of the string.
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*
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* Returned Value:
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* Upon completion, strchr() returns a pointer to the byte, or a null
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* pointer if the byte was not found.
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*
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****************************************************************************/
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#if !defined(CONFIG_LIBC_ARCH_STRCHR) && defined(LIBC_BUILD_STRCHR)
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#undef strchr
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no_builtin("strchr")
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nosanitize_address
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FAR char *strchr(FAR const char *s, int c)
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{
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FAR const unsigned char *s1 = (FAR const unsigned char *)s;
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FAR unsigned long *aligned_addr;
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unsigned char i = c;
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unsigned long mask;
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unsigned long j;
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/* Special case for finding 0. */
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if (!i)
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{
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while (UNALIGNED(s1))
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{
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if (!*s1)
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{
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return (FAR char *)s1;
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}
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s1++;
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}
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/* Operate a word at a time. */
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aligned_addr = (FAR unsigned long *)s1;
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while (!DETECTNULL(*aligned_addr))
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{
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aligned_addr++;
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}
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/* Found the end of string. */
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s1 = (FAR const unsigned char *)aligned_addr;
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while (*s1)
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{
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s1++;
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}
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return (FAR char *)s1;
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}
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/* All other bytes. Align the pointer, then search a long at a time. */
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while (UNALIGNED(s1))
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{
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if (!*s1)
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{
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return NULL;
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}
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if (*s1 == i)
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{
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return (FAR char *)s1;
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}
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s1++;
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}
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mask = i;
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for (j = 8; j < LBLOCKSIZE * 8; j <<= 1)
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{
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mask = (mask << j) | mask;
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}
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aligned_addr = (FAR unsigned long *)s1;
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while (!DETECTNULL(*aligned_addr) && !DETECTCHAR(*aligned_addr, mask))
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{
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aligned_addr++;
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}
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/* The block of bytes currently pointed to by aligned_addr
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* contains either a null or the target char, or both. We
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* catch it using the bytewise search.
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*/
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s1 = (FAR unsigned char *)aligned_addr;
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while (*s1 && *s1 != i)
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{
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s1++;
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}
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if (*s1 == i)
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{
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return (FAR char *)s1;
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}
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return NULL;
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}
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#endif
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