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/*

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;

}