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82 lines
2.2 KiB
C
82 lines
2.2 KiB
C
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/* bzero -- set a block of memory to zero.
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For Intel 80x86, x>=3.
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Copyright (C) 1991, 1992, 1993 Free Software Foundation, Inc.
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Contributed by Torbjorn Granlund (tege@sics.se).
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 675 Mass Ave,
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Cambridge, MA 02139, USA. */
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#include <ansidecl.h>
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#include <string.h>
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#include <memcopy.h>
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#undef bzero
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#ifdef __GNUC__
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void
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DEFUN(bzero, (dstpp, len),
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PTR dstpp AND size_t len)
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{
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/* N.B.: This code is almost verbatim from memset.c. */
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unsigned long int dstp = (unsigned long int) dstpp;
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/* This explicit register allocation
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improves code very much indeed. */
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register op_t x asm("ax");
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x = 0;
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/* Clear the direction flag, so filling will move forward. */
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asm volatile("cld");
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/* This threshold value is optimal. */
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if (len >= 12)
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{
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/* Adjust LEN for the bytes handled in the first loop. */
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len -= (-dstp) % OPSIZ;
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/* There are at least some bytes to set.
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No need to test for LEN == 0 in this alignment loop. */
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/* Fill bytes until DSTP is aligned on a longword boundary. */
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asm volatile("rep\n"
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"stosb" /* %0, %2, %3 */ :
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"=D" (dstp) :
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"0" (dstp), "c" ((-dstp) % OPSIZ), "a" (x) :
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"cx");
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/* Fill longwords. */
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asm volatile("rep\n"
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"stosl" /* %0, %2, %3 */ :
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"=D" (dstp) :
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"0" (dstp), "c" (len / OPSIZ), "a" (x) :
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"cx");
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len %= OPSIZ;
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}
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/* Write the last few bytes. */
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asm volatile("rep\n"
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"stosb" /* %0, %2, %3 */ :
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"=D" (dstp) :
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"0" (dstp), "c" (len), "a" (x) :
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"cx");
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}
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#else
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#include <sysdeps/generic/bzero.c>
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#endif
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