2008-05-26 Eric Blake <ebb9@byu.net>

Optimize the generic and x86 strlen.
        * libc/string/strlen.c (strlen) [!__OPTIMIZE_SIZE__]: Pre-align
        data so unaligned searches aren't penalized.
        * libc/machine/i386/strlen.S (strlen) [!__OPTIMIZE_SIZE__]:
        Word operations are faster than repnz byte searches.

newlib/ChangeLog

@@ -1,3 +1,11 @@
+2008-05-26  Eric Blake  <ebb9@byu.net>
+
+	Optimize the generic and x86 strlen.
+	* libc/string/strlen.c (strlen) [!__OPTIMIZE_SIZE__]: Pre-align
+	data so unaligned searches aren't penalized.
+	* libc/machine/i386/strlen.S (strlen) [!__OPTIMIZE_SIZE__]:
+	Word operations are faster than repnz byte searches.
+
 2008-05-23  Corinna Vinschen  <corinna@vinschen.de>
 
 	* libc/include/sys/_default_fcntl.h: Include <sys/time.h> on Cygwin.

newlib/libc/machine/i386/strlen.S

@@ -1,6 +1,6 @@
 /*
  * ====================================================
- * Copyright (C) 1998, 2002 by Red Hat Inc. All rights reserved.
+ * Copyright (C) 1998, 2002, 2008 by Red Hat Inc. All rights reserved.
  *
  * Permission to use, copy, modify, and distribute this
  * software is freely granted, provided that this notice
@@ -20,12 +20,75 @@ SYM (strlen):
 	pushl edi
 	movl 8(ebp),edx
 
+#ifdef __OPTIMIZE_SIZE__
 	cld
 	movl edx,edi
 	movl $4294967295,ecx
 	xor eax,eax
 	repnz
 	scasb
+#else
+/* Modern x86 hardware is much faster at double-word
+   manipulation than with bytewise repnz scasb.  */
+
+/* Do byte-wise checks until string is aligned.  */
+	movl edx,edi
+	test $3,edi
+	je L5
+	movb (edi),cl
+	incl edi
+	testb cl,cl
+	je L15
+
+	test $3,edi
+	je L5
+	movb (edi),cl
+	incl edi
+	testb cl,cl
+	je L15
+
+	test $3,edi
+	je L5
+	movb (edi),cl
+	incl edi
+	testb cl,cl
+	je L15
+
+L5:
+	subl $4,edi
+
+/* loop performing 4 byte mask checking for desired 0 byte */
+	.p2align 4,,7
+L10:
+	addl $4,edi
+	movl (edi),ecx
+	leal -16843009(ecx),eax
+	notl ecx
+	andl ecx,eax
+	testl $-2139062144,eax
+	je L10
+
+/* Find which of four bytes is 0.  */
+	notl ecx
+	incl edi
+
+	testb cl,cl
+	je L15
+	incl edi
+	shrl $8,ecx
+
+	testb cl,cl
+	je L15
+	incl edi
+	shrl $8,ecx
+
+	testb cl,cl
+	je L15
+	incl edi
+
+#endif
+
+L15:
 	subl edx,edi
 	leal -1(edi),eax
 

newlib/libc/string/strlen.c

@@ -57,32 +57,32 @@ size_t
 _DEFUN (strlen, (str),
 	_CONST char *str)
 {
-#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
   _CONST char *start = str;
 
-  while (*str)
+#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
-    str++;
-
-  return str - start;
-#else
-  _CONST char *start = str;
   unsigned long *aligned_addr;
 
-  if (!UNALIGNED (str))
+  /* Align the pointer, so we can search a word at a time.  */
+  while (UNALIGNED (str))
     {
-      /* If the string is word-aligned, we can check for the presence of 
+      if (!*str)
-         a null in each word-sized block.  */
+	return str - start;
-      aligned_addr = (unsigned long*)str;
+      str++;
-      while (!DETECTNULL (*aligned_addr))
-        aligned_addr++;
-
-      /* Once a null is detected, we check each byte in that block for a
-         precise position of the null.  */
-      str = (char*)aligned_addr;
     }
 
+  /* If the string is word-aligned, we can check for the presence of
+     a null in each word-sized block.  */
+  aligned_addr = (unsigned long *)str;
+  while (!DETECTNULL (*aligned_addr))
+    aligned_addr++;
+
+  /* Once a null is detected, we check each byte in that block for a
+     precise position of the null.  */
+  str = (char *) aligned_addr;
+
+#endif /* not PREFER_SIZE_OVER_SPEED */
+
   while (*str)
     str++;
   return str - start;
-#endif /* not PREFER_SIZE_OVER_SPEED */
 }