89 lines
1.9 KiB
C
89 lines
1.9 KiB
C
/*
|
|
FUNCTION
|
|
<<strlen>>---character string length
|
|
|
|
INDEX
|
|
strlen
|
|
|
|
ANSI_SYNOPSIS
|
|
#include <string.h>
|
|
size_t strlen(const char *<[str]>);
|
|
|
|
TRAD_SYNOPSIS
|
|
#include <string.h>
|
|
size_t strlen(<[str]>)
|
|
char *<[src]>;
|
|
|
|
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
|
|
_DEFUN (strlen, (str),
|
|
_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;
|
|
}
|