Module Name: src
Committed By: dsl
Date: Sat Aug 1 20:47:02 UTC 2009
Modified Files:
src/common/lib/libc/arch/x86_64/string: memchr.S
Log Message:
In the misaligned case, xor the read word with the target pattern
before making the unwanted bytes non-zero.
Means that memchr(buf, 0xff) is no longer a special case.
To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 src/common/lib/libc/arch/x86_64/string/memchr.S
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/common/lib/libc/arch/x86_64/string/memchr.S
diff -u src/common/lib/libc/arch/x86_64/string/memchr.S:1.4 src/common/lib/libc/arch/x86_64/string/memchr.S:1.5
--- src/common/lib/libc/arch/x86_64/string/memchr.S:1.4 Mon Jul 20 15:21:00 2009
+++ src/common/lib/libc/arch/x86_64/string/memchr.S Sat Aug 1 20:47:02 2009
@@ -1,4 +1,4 @@
-/* $NetBSD: memchr.S,v 1.4 2009/07/20 15:21:00 christos Exp $ */
+/* $NetBSD: memchr.S,v 1.5 2009/08/01 20:47:02 dsl Exp $ */
/*-
* Copyright (c) 2009 The NetBSD Foundation, Inc.
@@ -32,7 +32,7 @@
#include <machine/asm.h>
#if defined(LIBC_SCCS)
- RCSID("$NetBSD: memchr.S,v 1.4 2009/07/20 15:21:00 christos Exp $")
+ RCSID("$NetBSD: memchr.S,v 1.5 2009/08/01 20:47:02 dsl Exp $")
#endif
/*
@@ -63,9 +63,9 @@
jae 30f /* jump if so */
movq (%rdi),%rax /* value to check */
-2:
addq $8,%rdi
xorq %rsi,%rax /* now looking for zeros */
+2:
mov %rax,%rcx
subq %r8,%rax /* x - 0x01 */
not %rcx
@@ -82,32 +82,25 @@
rep
ret /* amd - no ret after jmp */
-/* Input misaligned, read aligned and kill low bits */
-/* (Getting a -1 is surprisingly hard work!) */
+/* Input misaligned, read aligned and make low bytes invalid */
20:
- xor %eax,%eax /* zeros all 64 bits */
mov %dil,%cl /* misalignment amount 1..7 (+high bits )*/
+ and $~7,%dil /* %rdi now start of word */
test %rdx,%rdx /* zero length, don't read */
jz 30f
- and $~7,%dil /* %rdi now start of word */
- lea -1(%rax),%r11 /* all 0xff */
- and $7,%cl /* 1..7 */
-
+ neg %cl /* 7..1 (+high bits) */
mov (%rdi),%rax /* word containing first byte */
- shl $3,%cl /* 8..56 */
- cmp %r11,%rsi /* searching for 0xff */
- jz 25f
-
- /* Searching for other than 0xff, set low bytes */
- shl %cl,%r11 /* 0xff in high (wanted) bytes */
- not %r11 /* 0xff in low (unwanted) bytes */
- or %r11,%rax /* low bytes now set */
- jmp 2b
+ addq $8,%rdi
+ and $7,%cl /* 7..1 */
-25: /* Searching for 0xff, clear low bytes */
- shl %cl,%r11 /* 0xff in high (wanted) bytes */
- and %r11,%rax /* low bytes now zero */
+ mov %r8,%r11 /* any value with bits in each byte */
+ shl $3,%cl /* 56..8 */
+ xorq %rsi,%rax /* now looking for zeros */
+
+ /* Set low bytes non-zero */
+ shr %cl,%r11 /* non-zero in unwanted bytes */
+ or %r11,%rax /* low bytes now set */
jmp 2b
/* Not found */
