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/*
FUNCTION
<<strlen>>---character string length
INDEX
strlen
SYNOPSIS
#include <string.h>
size_t strlen(const char *<[str]>);
DESCRIPTION
The <<strlen>> function works out the length of the string
starting at <<*<[str]>>> by counting chararacters until it
reaches a <<NULL>> character.
RETURNS
<<strlen>> returns the character count.
PORTABILITY
<<strlen>> is ANSI C.
<<strlen>> requires no supporting OS subroutines.
QUICKREF
strlen ansi pure
*/
#include <_ansi.h>
#include <string.h>
#include <limits.h>
#define LBLOCKSIZE (sizeof (long))
#define UNALIGNED(X) ((long)X & (LBLOCKSIZE - 1))
#if LONG_MAX == 2147483647L
#define DETECTNULL(X) (((X) - 0x01010101) & ~(X) & 0x80808080)
#else
#if LONG_MAX == 9223372036854775807L
/* Nonzero if X (a long int) contains a NULL byte. */
#define DETECTNULL(X) (((X) - 0x0101010101010101) & ~(X) & 0x8080808080808080)
#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
size_t
strlen (const char *str)
{
const char *start = str;
#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
unsigned long *aligned_addr;
/* Align the pointer, so we can search a word at a time. */
while (UNALIGNED (str))
{
if (!*str)
return str - start;
str++;
}
/* If the string is word-aligned, we can check for the presence of
a null in each word-sized block. */
aligned_addr = (unsigned long *)str;
while (!DETECTNULL (*aligned_addr))
aligned_addr++;
/* Once a null is detected, we check each byte in that block for a
precise position of the null. */
str = (char *) aligned_addr;
#endif /* not PREFER_SIZE_OVER_SPEED */
while (*str)
str++;
return str - start;
}
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