106 lines
3 KiB
C
106 lines
3 KiB
C
/****************************************************************************
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* libs/libc/string/lib_strlen.c
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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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 <sys/types.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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#ifdef CONFIG_LIBC_STRING_OPTIMIZE
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#define LBLOCKSIZE (sizeof(long))
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#define UNALIGNED(x) ((long)(uintptr_t)(x) & (LBLOCKSIZE - 1))
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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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#endif
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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#if !defined(CONFIG_LIBC_ARCH_STRLEN) && defined(LIBC_BUILD_STRLEN)
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#undef strlen /* See mm/README.txt */
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nosanitize_address
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size_t strlen(FAR const char *s)
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{
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#ifdef CONFIG_LIBC_STRING_OPTIMIZE
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FAR const char *start = s;
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FAR unsigned long *aligned_addr;
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/* Align the pointer, so we can search a word at a time. */
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while (UNALIGNED(s))
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{
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if (!*s)
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{
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return s - start;
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}
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s++;
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}
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/* If the string is word-aligned, we can check for the presence of
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* a null in each word-sized block.
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*/
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aligned_addr = (FAR unsigned long *)s;
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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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/* Once a null is detected, we check each byte in that block for a
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* precise position of the null.
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*/
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s = (FAR char *)aligned_addr;
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while (*s)
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{
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s++;
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}
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return s - start;
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#else
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FAR const char *sc;
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for (sc = s; *sc != '\0'; ++sc);
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return sc - s;
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#endif
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}
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#endif
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