/* Copyright (C) 1991-2018 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

/* 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)