Import glibc-mainline for 2006-08-16

git-svn-id: svn://svn.eglibc.org/fsf/trunk@4 7b3dc134-2b1b-0410-93df-9e9f96275f8d

1 files changed, 301 insertions, 0 deletions

diff --git a/libc/sysdeps/i386/strchr.S b/libc/sysdeps/i386/strchr.S
new file mode 100644
index 000000000..93b4cce8d
--- /dev/null
+++ b/libc/sysdeps/i386/strchr.S
@@ -0,0 +1,301 @@
+/* strchr (str, ch) -- Return pointer to first occurrence of CH in STR.
+   For Intel 80x86, x>=3.
+   Copyright (C) 1994-1997,1999,2000,2002,2003,2005
+   Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>
+   Some optimisations by Alan Modra <Alan@SPRI.Levels.UniSA.Edu.Au>
+
+   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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <sysdep.h>
+#include "asm-syntax.h"
+#include "bp-sym.h"
+#include "bp-asm.h"
+
+#define PARMS	LINKAGE+4		/* space for 1 saved reg */
+#define RTN	PARMS
+#define STR	RTN+RTN_SIZE
+#define CHR	STR+PTR_SIZE
+
+	.text
+ENTRY (BP_SYM (strchr))
+	ENTER
+
+	pushl %edi		/* Save callee-safe registers used here.  */
+	cfi_adjust_cfa_offset (4)
+	cfi_rel_offset (edi, 0)
+	movl STR(%esp), %eax
+	movl CHR(%esp), %edx
+	CHECK_BOUNDS_LOW (%eax, STR(%esp))
+
+	/* 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 it is c|c|0|0 */
+	movw %cx, %dx		/* and finally c|c|c|c */
+
+	/* Before we start with the main loop we process single bytes
+	   until the source pointer is aligned.  This has two reasons:
+	   1. aligned 32-bit memory access is faster
+	   and (more important)
+	   2. we process in the main loop 32 bit in one step although
+	      we don't know the end of the string.  But accessing at
+	      4-byte alignment guarantees that we never access illegal
+	      memory if this would not also be done by the trivial
+	      implementation (this is because all processor inherent
+	      boundaries are multiples of 4.  */
+
+	testb $3, %al		/* correctly aligned ? */
+	jz L(11)		/* yes => begin loop */
+	movb (%eax), %cl	/* load byte in question (we need it twice) */
+	cmpb %cl, %dl		/* compare byte */
+	je L(6)			/* target found => return */
+	testb %cl, %cl		/* is NUL? */
+	jz L(2)			/* yes => return NULL */
+	incl %eax		/* increment pointer */
+
+	testb $3, %al		/* correctly aligned ? */
+	jz L(11)		/* yes => begin loop */
+	movb (%eax), %cl	/* load byte in question (we need it twice) */
+	cmpb %cl, %dl		/* compare byte */
+	je L(6)			/* target found => return */
+	testb %cl, %cl		/* is NUL? */
+	jz L(2)			/* yes => return NULL */
+	incl %eax		/* increment pointer */
+
+	testb $3, %al		/* correctly aligned ? */
+	jz L(11)		/* yes => begin loop */
+	movb (%eax), %cl	/* load byte in question (we need it twice) */
+	cmpb %cl, %dl		/* compare byte */
+	je L(6)			/* target found => return */
+	testb %cl, %cl		/* is NUL? */
+	jz L(2)			/* yes => return NULL */
+	incl %eax		/* increment pointer */
+
+	/* No we have reached alignment.  */
+	jmp L(11)		/* begin loop */
+
+      /* 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):	addl $16, %eax		/* adjust pointer for whole round */
+
+L(11):	movl (%eax), %ecx	/* get word (= 4 bytes) in question */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* C */
+
+	/* 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(7)
+
+	/* 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(7)		/* found it => return pointer */
+
+	/* Now we made sure the dword does not contain the character we are
+	   looking for.  But because we deal with strings we have to check
+	   for the end of string before testing the next dword.  */
+
+	xorl %edx, %ecx		/* restore original dword without reload */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+	jnc L(2)		/* highest byte is NUL => return NULL */
+	xorl %ecx, %edi		/* (word+magic)^word */
+	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(2)		/* found NUL => return NULL */
+
+	movl 4(%eax), %ecx	/* get word (= 4 bytes) in question */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* C */
+	jnc L(71)		/* 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(71)		/* found it => return pointer */
+	xorl %edx, %ecx		/* restore original dword without reload */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+	jnc L(2)		/* highest byte is NUL => return NULL */
+	xorl %ecx, %edi		/* (word+magic)^word */
+	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(2)		/* found NUL => return NULL */
+
+	movl 8(%eax), %ecx	/* get word (= 4 bytes) in question */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* C */
+	jnc L(72)		/* 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(72)		/* found it => return pointer */
+	xorl %edx, %ecx		/* restore original dword without reload */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+	jnc L(2)		/* highest byte is NUL => return NULL */
+	xorl %ecx, %edi		/* (word+magic)^word */
+	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(2)		/* found NUL => return NULL */
+
+	movl 12(%eax), %ecx	/* get word (= 4 bytes) in question */
+	xorl %edx, %ecx		/* XOR with word c|c|c|c => bytes of str == c
+				   are now 0 */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* C */
+	jnc L(73)		/* 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(73)		/* found it => return pointer */
+	xorl %edx, %ecx		/* restore original dword without reload */
+	movl $0xfefefeff, %edi	/* magic value */
+	addl %ecx, %edi		/* add the magic value to the word.  We get
+				   carry bits reported for each byte which
+				   is *not* 0 */
+	jnc L(2)		/* highest byte is NUL => return NULL */
+	xorl %ecx, %edi		/* (word+magic)^word */
+	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.  */
+	jz L(1)			/* no NUL found => restart loop */
+
+L(2):	/* Return NULL.  */
+	xorl %eax, %eax
+	RETURN_NULL_BOUNDED_POINTER
+	popl %edi		/* restore saved register content */
+	cfi_adjust_cfa_offset (-4)
+	cfi_restore (edi)
+
+	LEAVE
+	RET_PTR
+
+	cfi_adjust_cfa_offset (4)
+	cfi_rel_offset (edi, 0)
+L(73):	addl $4, %eax		/* adjust pointer */
+L(72):	addl $4, %eax
+L(71):	addl $4, %eax
+
+	/* We now scan for the byte in which the character was matched.
+	   But we have to take care of the case that a NUL char is
+	   found before this in the dword.  Note that we XORed %ecx
+	   with the byte we're looking for, therefore the tests below look
+	   reversed.  */
+
+L(7):	testb %cl, %cl		/* is first byte C? */
+	jz L(6)			/* yes => return pointer */
+	cmpb %dl, %cl		/* is first byte NUL? */
+	je L(2)			/* yes => return NULL */
+	incl %eax		/* it's not in the first byte */
+
+	testb %ch, %ch		/* is second byte C? */
+	jz L(6)			/* yes => return pointer */
+	cmpb %dl, %ch		/* is second byte NUL? */
+	je L(2)			/* yes => return NULL? */
+	incl %eax		/* it's not in the second byte */
+
+	shrl $16, %ecx		/* make upper byte accessible */
+	testb %cl, %cl		/* is third byte C? */
+	jz L(6)			/* yes => return pointer */
+	cmpb %dl, %cl		/* is third byte NUL? */
+	je L(2)			/* yes => return NULL */
+
+	/* It must be in the fourth byte and it cannot be NUL.  */
+	incl %eax
+
+L(6):
+	CHECK_BOUNDS_HIGH (%eax, STR(%esp), jb)
+	RETURN_BOUNDED_POINTER (STR(%esp))
+	popl %edi		/* restore saved register content */
+	cfi_adjust_cfa_offset (-4)
+	cfi_restore (edi)
+
+	LEAVE
+	RET_PTR
+END (BP_SYM (strchr))
+
+weak_alias (BP_SYM (strchr), BP_SYM (index))
+libc_hidden_builtin_def (strchr)