bzero.c

来自「一个C源代码分析器」· C语言 代码 · 共 82 行

/* Copyright (C) 1991 Free Software Foundation, Inc.
   Contributed by Torbjorn Granlund ([e-mail]).
   
This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 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
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <ansidecl.h>
#include <string.h>
#include <memcopy.h>

/* Set N bytes of S to 0.  */
void
DEFUN(bzero, (s, n), PTR s AND size_t len)
{
  long int dstp = (long int) s;
  CONST op_t zero = 0;

  if (len >= 8)
    {
      size_t xlen;

      /* There are at least some bytes to zero.  No need to test
	 for LEN == 0 in this alignment loop.  */
      while (dstp % OPSIZ != 0)
	{
	  ((byte *) dstp)[0] = 0;
	  dstp += 1;
	  len -= 1;
	}

      /* Write 8 op_t per iteration until less than 8 op_t remain.  */
      xlen = len / (OPSIZ * 8);
      while (xlen != 0)
	{
	  ((op_t *) dstp)[0] = zero;
	  ((op_t *) dstp)[1] = zero;
	  ((op_t *) dstp)[2] = zero;
	  ((op_t *) dstp)[3] = zero;
	  ((op_t *) dstp)[4] = zero;
	  ((op_t *) dstp)[5] = zero;
	  ((op_t *) dstp)[6] = zero;
	  ((op_t *) dstp)[7] = zero;
	  dstp += 8 * OPSIZ;
	  xlen -= 1;
	}
      len %= OPSIZ * 8;

      /* Write 1 op_t per iteration until less than op_t remain.  */
      xlen = len / OPSIZ;
      while (xlen != 0)
	{
	  ((op_t *) dstp)[0] = zero;
	  dstp += OPSIZ;
	  xlen -= 1;
	}
      len %= OPSIZ;
    }

  /* Write the last few bytes.  */
  while (len != 0)
    {
      ((byte *) dstp)[0] = 0;
      dstp += 1;
      len -= 1;
    }
}