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authorUlrich Drepper <drepper@redhat.com>1999-01-16 17:09:04 +0000
committerUlrich Drepper <drepper@redhat.com>1999-01-16 17:09:04 +0000
commit482eec0d1188823ad93247f79bf965886e8bd4f7 (patch)
tree5a3157c41a1310f5440de77f841753a32bb1444d /sysdeps/i386/rawmemchr.S
parent37a87f834a459f6136ff44c7887b013d1ae0f6be (diff)
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Update.
1999-01-16  Ulrich Drepper  <drepper@cygnus.com>

	* elf/Makefile (tests): Add loadtest.
	Add rules to generate test modules.
	* Makeconfig (+link): Add $(LDFLAGS-$(@F)) to command line.
	* elf/loadtest.c: New file.
	* elf/testobj1.c: New file.
	* elf/testobj2.c: New file.
	* elf/testobj3.c: New file.

	* elf/dl-close.c: Correct removing module from global list.

	* elf/dl-open.c: Add debugging code.

	* include/string.h: Add __rawmemchr prototype.
	* string/Makefile (routines): Add rawmemchr.
	* string/Versions [GLIBC_2.1]: Add __rawmemchr and rawmemchr.
	* string/string.h: Add prototype for rawmemchr.
	* string/bits/string2.h: Optimize strchr with rawmemchr.
	* sysdeps/generic/rawmemchr.c: New file.
	* sysdeps/i386/rawmemchr.c: New file.
	* sysdeps/i386/i486/bits/string.h: Add rawmemchr inline code.
	Optimize strchr with rawmemchr.

	* sysdeps/unix/sysv/linux/bits/posix_opt.h: Define _LFS_LARGEFILE,
	_LFS64_LARGEFILE, and _LFS64_STDIO for Unix98.

1999-01-14  Andreas Jaeger  <aj@arthur.rhein-neckar.de>

	* nis/nis_error.c (nis_errlist): Fix capitilasation.
Diffstat (limited to 'sysdeps/i386/rawmemchr.S')
-rw-r--r--sysdeps/i386/rawmemchr.S218
1 files changed, 218 insertions, 0 deletions
diff --git a/sysdeps/i386/rawmemchr.S b/sysdeps/i386/rawmemchr.S
new file mode 100644
index 0000000000..83626e0473
--- /dev/null
+++ b/sysdeps/i386/rawmemchr.S
@@ -0,0 +1,218 @@
+/* rawmemchr (str, ch) -- Return pointer to first occurrence of CH in STR.
+   For Intel 80x86, x>=3.
+   Copyright (C) 1994, 95, 96, 97, 98, 99 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>
+   Optimised a little by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au>
+
+   This version is developed using the same algorithm as the fast C
+   version which carries the following introduction:
+
+   Based on strlen implementation by Torbjorn Granlund (tege@sics.se),
+   with help from Dan Sahlin (dan@sics.se) and
+   commentary by Jim Blandy (jimb@ai.mit.edu);
+   adaptation to memchr suggested by Dick Karpinski (dick@cca.ucsf.edu),
+   and implemented by Roland McGrath (roland@ai.mit.edu).
+
+   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., 59 Temple Place - Suite 330,
+   Boston, MA 02111-1307, USA.  */
+
+#include <sysdep.h>
+#include "asm-syntax.h"
+
+/*
+   INPUT PARAMETERS:
+   str		(sp + 4)
+   c		(sp + 8)
+*/
+
+	.text
+ENTRY (__rawmemchr)
+	/* Save callee-safe register used in this function.  */
+	pushl %edi
+
+	/* Load parameters into registers.  */
+	movl 8(%esp), %eax	/* str: pointer to memory block.  */
+	movl 12(%esp), %edx	/* c: byte we are looking for.  */
+
+	/* At the moment %edx contains C.  What we need for the
+	   algorithm is C in all bytes of the dword.  Avoid
+	   operations on 16 bit words because these require an
+	   prefix byte (and one more cycle).  */
+	movb %dl, %dh		/* Now it is 0|0|c|c */
+	movl %edx, %ecx
+	shll $16, %edx		/* Now c|c|0|0 */
+	movw %cx, %dx		/* And finally c|c|c|c */
+
+	/* Better performance can be achieved if the word (32
+	   bit) memory access is aligned on a four-byte-boundary.
+	   So process first bytes one by one until boundary is
+	   reached. Don't use a loop for better performance.  */
+
+	testb $3, %al		/* correctly aligned ? */
+	je L(1)			/* yes => begin loop */
+	cmpb %dl, (%eax)	/* compare byte */
+	je L(9)			/* target found => return */
+	incl %eax		/* increment source pointer */
+
+	testb $3, %al		/* correctly aligned ? */
+	je L(1)			/* yes => begin loop */
+	cmpb %dl, (%eax)	/* compare byte */
+	je L(9)			/* target found => return */
+	incl %eax		/* increment source pointer */
+
+	testb $3, %al		/* correctly aligned ? */
+	je L(1)			/* yes => begin loop */
+	cmpb %dl, (%eax)	/* compare byte */
+	je L(9)			/* target found => return */
+	incl %eax		/* increment source pointer */
+
+      /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to
+	 change any of the hole bits of LONGWORD.
+
+	 1) Is this safe?  Will it catch all the zero bytes?
+	 Suppose there is a byte with all zeros.  Any carry bits
+	 propagating from its left will fall into the hole at its
+	 least significant bit and stop.  Since there will be no
+	 carry from its most significant bit, the LSB of the
+	 byte to the left will be unchanged, and the zero will be
+	 detected.
+
+	 2) Is this worthwhile?  Will it ignore everything except
+	 zero bytes?  Suppose every byte of LONGWORD has a bit set
+	 somewhere.  There will be a carry into bit 8.	If bit 8
+	 is set, this will carry into bit 16.  If bit 8 is clear,
+	 one of bits 9-15 must be set, so there will be a carry
+	 into bit 16.  Similarly, there will be a carry into bit
+	 24.  If one of bits 24-31 is set, there will be a carry
+	 into bit 32 (=carry flag), so all of the hole bits will
+	 be changed.
+
+	 3) But wait!  Aren't we looking for C, not zero?
+	 Good point.  So what we do is XOR LONGWORD with a longword,
+	 each of whose bytes is C.  This turns each byte that is C
+	 into a zero.  */
+
+
+	/* Each round the main loop processes 16 bytes.  */
+	ALIGN (4)
+
+L(1):	movl (%eax), %ecx	/* get word (= 4 bytes) in question */
+	movl $0xfefefeff, %edi	/* magic value */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+
+	/* According to the algorithm we had to reverse the effect of the
+	   XOR first and then test the overflow bits.  But because the
+	   following XOR would destroy the carry flag and it would (in a
+	   representation with more than 32 bits) not alter then last
+	   overflow, we can now test this condition.  If no carry is signaled
+	   no overflow must have occurred in the last byte => it was 0.	*/
+	jnc L(8)
+
+	/* We are only interested in carry bits that change due to the
+	   previous add, so remove original bits */
+	xorl %ecx, %edi		/* ((word^charmask)+magic)^(word^charmask) */
+
+	/* Now test for the other three overflow bits.  */
+	orl $0xfefefeff, %edi	/* set all non-carry bits */
+	incl %edi		/* add 1: if one carry bit was *not* set
+				   the addition will not result in 0.  */
+
+	/* If at least one byte of the word is C we don't get 0 in %edi.  */
+	jnz L(8)		/* found it => return pointer */
+
+	/* This process is unfolded four times for better performance.
+	   we don't increment the source pointer each time.  Instead we
+	   use offsets and increment by 16 in each run of the loop.  But
+	   before probing for the matching byte we need some extra code
+	   (following LL(13) below).  Even the len can be compared with
+	   constants instead of decrementing each time.  */
+
+	movl 4(%eax), %ecx	/* get word (= 4 bytes) in question */
+	movl $0xfefefeff, %edi	/* magic value */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+	jnc L(7)		/* highest byte is C => return pointer */
+	xorl %ecx, %edi		/* ((word^charmask)+magic)^(word^charmask) */
+	orl $0xfefefeff, %edi	/* set all non-carry bits */
+	incl %edi		/* add 1: if one carry bit was *not* set
+				   the addition will not result in 0.  */
+	jnz L(7)		/* found it => return pointer */
+
+	movl 8(%eax), %ecx	/* get word (= 4 bytes) in question */
+	movl $0xfefefeff, %edi	/* magic value */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+	jnc L(6)		/* highest byte is C => return pointer */
+	xorl %ecx, %edi		/* ((word^charmask)+magic)^(word^charmask) */
+	orl $0xfefefeff, %edi	/* set all non-carry bits */
+	incl %edi		/* add 1: if one carry bit was *not* set
+				   the addition will not result in 0.  */
+	jnz L(6)		/* found it => return pointer */
+
+	movl 12(%eax), %ecx	/* get word (= 4 bytes) in question */
+	movl $0xfefefeff, %edi	/* magic value */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+	jnc L(5)		/* highest byte is C => return pointer */
+	xorl %ecx, %edi		/* ((word^charmask)+magic)^(word^charmask) */
+	orl $0xfefefeff, %edi	/* set all non-carry bits */
+	incl %edi		/* add 1: if one carry bit was *not* set
+				   the addition will not result in 0.  */
+	jnz L(5)		/* found it => return pointer */
+
+	/* Adjust both counters for a full round, i.e. 16 bytes.  */
+	addl $16, %eax
+	jmp L(1)
+	/* add missing source pointer increments */
+L(5):	addl $4, %eax
+L(6):	addl $4, %eax
+L(7):	addl $4, %eax
+
+	/* Test for the matching byte in the word.  %ecx contains a NUL
+	   char in the byte which originally was the byte we are looking
+	   at.  */
+L(8):	testb %cl, %cl		/* test first byte in dword */
+	jz L(9)			/* if zero => return pointer */
+	incl %eax		/* increment source pointer */
+
+	testb %ch, %ch		/* test second byte in dword */
+	jz L(9)			/* if zero => return pointer */
+	incl %eax		/* increment source pointer */
+
+	testl $0xff0000, %ecx	/* test third byte in dword */
+	jz L(9)			/* if zero => return pointer */
+	incl %eax		/* increment source pointer */
+
+	/* No further test needed we we know it is one of the four bytes.  */
+
+L(9):	popl %edi		/* pop saved register */
+
+	ret
+END (__rawmemchr)
+weak_alias (__rawmemchr, rawmemchr)