strlen.c
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/* Copyright (C) 1991-2019 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Written by Torbjorn Granlund (tege@sics.se),
with help from Dan Sahlin (dan@sics.se);
commentary by Jim Blandy (jimb@ai.mit.edu).
The GNU C Library 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.
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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <string.h>
#include <stdlib.h>
#undef strlen
#ifndef STRLEN
# define STRLEN strlen
#endif
size_t strlen(const char *str)
{
size_t i=0;
if (!str) return 0;
while (str[i])
i++;
return i;
}
///* Return the length of the null-terminated string STR. Scan for
// the null terminator quickly by testing four bytes at a time. */
//size_t
//STRLEN (const char *str)
//{
// const char *char_ptr;
// const unsigned long int *longword_ptr;
// unsigned long int longword, himagic, lomagic;
// /* Handle the first few characters by reading one character at a time.
// Do this until CHAR_PTR is aligned on a longword boundary. */
// for (char_ptr = str; ((unsigned long int) char_ptr
// & (sizeof (longword) - 1)) != 0;
// ++char_ptr)
// if (*char_ptr == '\0')
// return char_ptr - str;
// /* All these elucidatory comments refer to 4-byte longwords,
// but the theory applies equally well to 8-byte longwords. */
// longword_ptr = (unsigned long int *) char_ptr;
// /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits
// the "holes." Note that there is a hole just to the left of
// each byte, with an extra at the end:
// bits: 01111110 11111110 11111110 11111111
// bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
// The 1-bits make sure that carries propagate to the next 0-bit.
// The 0-bits provide holes for carries to fall into. */
// himagic = 0x80808080L;
// lomagic = 0x01010101L;
// if (sizeof (longword) > 4)
// {
// /* 64-bit version of the magic. */
// /* Do the shift in two steps to avoid a warning if long has 32 bits. */
// himagic = ((himagic << 16) << 16) | himagic;
// lomagic = ((lomagic << 16) << 16) | lomagic;
// }
// if (sizeof (longword) > 8)
// abort ();
// /* Instead of the traditional loop which tests each character,
// 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 zero. */
// for (;;)
// {
// longword = *longword_ptr++;
// if (((longword - lomagic) & ~longword & himagic) != 0)
// {
// /* Which of the bytes was the zero? If none of them were, it was
// a misfire; continue the search. */
// const char *cp = (const char *) (longword_ptr - 1);
// if (cp[0] == 0)
// return cp - str;
// if (cp[1] == 0)
// return cp - str + 1;
// if (cp[2] == 0)
// return cp - str + 2;
// if (cp[3] == 0)
// return cp - str + 3;
// if (sizeof (longword) > 4)
// {
// if (cp[4] == 0)
// return cp - str + 4;
// if (cp[5] == 0)
// return cp - str + 5;
// if (cp[6] == 0)
// return cp - str + 6;
// if (cp[7] == 0)
// return cp - str + 7;
// }
// }
// }
//}
////libc_hidden_builtin_def (strlen)