diff --git a/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S b/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
index 6d9951e..028c6d3 100644
--- a/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
+++ b/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
@@ -34,6 +34,9 @@ ENTRY (STRCAT)
 	mov	%rdx, %r8
 # endif
 
+/* Inline corresponding strlen file, temporary until new strcpy
+   implementation gets merged.  */
+
 	xor	%rax, %rax
 	mov	%edi, %ecx
 	and	$0x3f, %ecx
diff --git a/sysdeps/x86_64/multiarch/strcat-ssse3.S b/sysdeps/x86_64/multiarch/strcat-ssse3.S
index 901e66f..8101b91 100644
--- a/sysdeps/x86_64/multiarch/strcat-ssse3.S
+++ b/sysdeps/x86_64/multiarch/strcat-ssse3.S
@@ -33,6 +33,10 @@ ENTRY (STRCAT)
 	mov	%rdx, %r8
 # endif
 
+
+/* Inline corresponding strlen file, temporary until new strcpy
+   implementation gets merged.  */
+
 	xor	%eax, %eax
 	cmpb	$0, (%rdi)
 	jz	L(exit_tail0)
diff --git a/sysdeps/x86_64/strcat.S b/sysdeps/x86_64/strcat.S
index 287ffd2..8bea6fb 100644
--- a/sysdeps/x86_64/strcat.S
+++ b/sysdeps/x86_64/strcat.S
@@ -21,6 +21,7 @@
 #include <sysdep.h>
 #include "asm-syntax.h"
 
+/* Will be removed when new strcpy implementation gets merged.  */
 
 	.text
 ENTRY (strcat)
diff --git a/sysdeps/x86_64/strlen.S b/sysdeps/x86_64/strlen.S
index e82fe8d..6abb3f0 100644
--- a/sysdeps/x86_64/strlen.S
+++ b/sysdeps/x86_64/strlen.S
@@ -1,5 +1,5 @@
 /* SSE2 version of strlen.
-   Copyright (C) 2012, 2013 Free Software Foundation, Inc.
+   Copyright (C) 2012-2013 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -18,12 +18,11 @@
 
 #include <sysdep.h>
 
-/* Long lived register are
-	strlen(s), strnlen(s, n):
+/* Long lived register in strlen(s), strnlen(s, n) are:
 
 	%xmm11 - zero
 	%rdi   - s
-	%r10  (s+n)	& (~(64-1))
+	%r10  (s+n) & (~(64-1))
 	%r11   s+n
 */
 
@@ -31,6 +30,7 @@
 .text
 ENTRY(strlen)
 
+/* Test 64 bytes from %rax for zero. Save result as bitmask in %rdx.  */
 #define FIND_ZERO	\
 	pcmpeqb	(%rax), %xmm8;	\
 	pcmpeqb	16(%rax), %xmm9;	\
@@ -73,9 +73,10 @@ L(n_nonzero):
 /* Offsets 4032-4047 will be aligned into 4032 thus fit into page.  */
 	cmpq	$4047, %rcx
 /* We cannot unify this branching as it would be ~6 cycles slower.  */
-	ja	L(next)
+	ja	L(cross_page)
 
 #ifdef AS_STRNLEN
+/* Test if end is among first 64 bytes.  */
 # define STRNLEN_PROLOG	\
 	mov	%r11, %rsi;	\
 	subq	%rax, %rsi;	\
@@ -86,6 +87,7 @@ L(n_nonzero):
 # define STRNLEN_PROLOG  andq $-64, %rax;
 #endif
 
+/* Ignore bits in mask that come before start of string.  */
 #define PROLOG(lab)	\
 	movq	%rdi, %rcx;	\
 	xorq	%rax, %rcx;	\
@@ -100,34 +102,37 @@ L(n_nonzero):
 	andq	$-16, %rax
 	FIND_ZERO
 #else
+	/* Test first 16 bytes unaligned.  */
 	movdqu	(%rax), %xmm12
 	pcmpeqb	%xmm8, %xmm12
 	pmovmskb	%xmm12, %edx
 	test	%edx, %edx
 	je 	L(next48_bytes)
-	bsfq	%rdx, %rax
+	bsf	%edx, %eax /* If eax is zeroed 16bit bsf can be used.  */
 	ret
 
 L(next48_bytes):
 /* Same as FIND_ZERO except we do not check first 16 bytes.  */
 	andq	$-16, %rax
-	pcmpeqb 16(%rax), %xmm9;
-	pcmpeqb 32(%rax), %xmm10;
-	pcmpeqb 48(%rax), %xmm11;
-	pmovmskb	%xmm9, %edx;
-	pmovmskb	%xmm10, %r8d;
-	pmovmskb	%xmm11, %ecx;
-	salq	$16, %rdx;
-	salq	$16, %rcx;
-	orq	%r8, %rcx;
-	salq	$32, %rcx;
-	orq	%rcx, %rdx;
+	pcmpeqb 16(%rax), %xmm9
+	pcmpeqb 32(%rax), %xmm10
+	pcmpeqb 48(%rax), %xmm11
+	pmovmskb	%xmm9, %edx
+	pmovmskb	%xmm10, %r8d
+	pmovmskb	%xmm11, %ecx
+	salq	$16, %rdx
+	salq	$16, %rcx
+	orq	%r8, %rcx
+	salq	$32, %rcx
+	orq	%rcx, %rdx
 #endif
 
-	PROLOG(loop)
+	/* When no zero byte is found xmm9-11 are zero so we do not have to
+	   zero them.  */
+	PROLOG(loop) 
 
 	.p2align 4
-L(next):
+L(cross_page):
 	andq	$-64, %rax
 	FIND_ZERO
 	PROLOG(loop_init)
@@ -168,7 +173,7 @@ L(loop):
 	.p2align 4
 L(exit_end):
 	cmp	%rax, %r11
-	je	L(first)
+	je	L(first) /* Do not read when end is at page boundary.  */
 	pxor	%xmm8, %xmm8
 	FIND_ZERO
 
@@ -190,6 +195,8 @@ L(exit):
 	ret
 
 #else
+
+	/* Main loop.  Unrolled twice to improve L2 cache performance on core2.  */
 	.p2align 4
 L(loop):
 
@@ -229,6 +236,4 @@ L(exit0):
 #endif
 
 END(strlen)
-#ifndef AS_STRLEN
 libc_hidden_builtin_def (strlen)
-#endif