GNU C Library master sources branch master updated. glibc-2.25-351-g402bf06

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http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=402bf0695218bbe290418b9486b1dd5fe284d903

commit 402bf0695218bbe290418b9486b1dd5fe284d903
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri May 19 10:46:29 2017 -0700

    x86: Optimize SSE2 memchr overflow calculation
    
    SSE2 memchr computes "edx + ecx - 16" where ecx is less than 16.  Use
    "edx - (16 - ecx)", instead of satured math, to avoid possible addition
    overflow.  This replaces
    
    	add	%ecx, %edx
    	sbb	%eax, %eax
    	or	%eax, %edx
    	sub	$16, %edx
    
    with
    
    	neg	%ecx
    	add	$16, %ecx
    	sub	%ecx, %edx
    
    It is the same for x86_64, except for rcx/rdx, instead of ecx/edx.
    
    	* sysdeps/i386/i686/multiarch/memchr-sse2.S (MEMCHR): Use
    	"edx + ecx - 16" to avoid possible addition overflow.
    	* sysdeps/x86_64/memchr.S (memchr): Likewise.

diff --git a/ChangeLog b/ChangeLog
index 3c8d9f1..b9fbdb8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2017-05-19  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* sysdeps/i386/i686/multiarch/memchr-sse2.S (MEMCHR): Use
+	"edx + ecx - 16" to avoid possible addition overflow.
+	* sysdeps/x86_64/memchr.S (memchr): Likewise.
+
 2017-05-19  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
 	* misc/Makefile (CFLAGS-vmsplice.c): Remove rule.
diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S
index e41f324..172d70d 100644
--- a/sysdeps/i386/i686/multiarch/memchr-sse2.S
+++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S
@@ -117,14 +117,12 @@ L(crosscache):
 
 # ifndef USE_AS_RAWMEMCHR
 	jnz	L(match_case2_prolog1)
-        /* Calculate the last acceptable address and check for possible
-           addition overflow by using satured math:
-           edx = ecx + edx
-           edx |= -(edx < ecx)  */
-	add	%ecx, %edx
-	sbb	%eax, %eax
-	or	%eax, %edx
-	sub	$16, %edx
+        /* "ecx" is less than 16.  Calculate "edx + ecx - 16" by using
+	   "edx - (16 - ecx)" instead of "(edx + ecx) - 16" to void
+	   possible addition overflow.  */
+	neg	%ecx
+	add	$16, %ecx
+	sub	%ecx, %edx
 	jbe	L(return_null)
 	lea	16(%edi), %edi
 # else
diff --git a/sysdeps/x86_64/memchr.S b/sysdeps/x86_64/memchr.S
index a205a25..f82e1c5 100644
--- a/sysdeps/x86_64/memchr.S
+++ b/sysdeps/x86_64/memchr.S
@@ -76,14 +76,12 @@ L(crosscache):
 
 	.p2align 4
 L(unaligned_no_match):
-        /* Calculate the last acceptable address and check for possible
-           addition overflow by using satured math:
-           rdx = rcx + rdx
-           rdx |= -(rdx < rcx)  */
-	add	%rcx, %rdx
-	sbb	%rax, %rax
-	or	%rax, %rdx
-	sub	$16, %rdx
+        /* "rcx" is less than 16.  Calculate "rdx + rcx - 16" by using
+	   "rdx - (16 - rcx)" instead of "(rdx + rcx) - 16" to void
+	   possible addition overflow.  */
+	neg	%rcx
+	add	$16, %rcx
+	sub	%rcx, %rdx
 	jbe	L(return_null)
 	add	$16, %rdi
 	sub	$64, %rdx

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                 |    6 ++++++
 sysdeps/i386/i686/multiarch/memchr-sse2.S |   14 ++++++--------
 sysdeps/x86_64/memchr.S                   |   14 ++++++--------
 3 files changed, 18 insertions(+), 16 deletions(-)


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