PowerPC LE strnlen

http://sourceware.org/ml/libc-alpha/2013-08/msg00098.html

The existing strnlen code has a number of defects, so this patch is more
than just adding little-endian support.  The changes here are similar to
those for memchr.

	* sysdeps/powerpc/powerpc64/power7/strnlen.S (strnlen): Add
	little-endian support.  Remove unnecessary "are we done" tests.
	Handle "s" wrapping around zero and extremely large "size".
	Correct main loop count.  Handle single left-over word from main
	loop inline rather than by using small_loop.  Correct comments.
	Delete "zero" tail, use "end_max" instead.
	* sysdeps/powerpc/powerpc32/power7/strnlen.S: Likewise.

2 files changed, 115 insertions, 102 deletions

diff --git a/sysdeps/powerpc/powerpc32/power7/strnlen.S b/sysdeps/powerpc/powerpc32/power7/strnlen.S
index ed088366a2..eb52afd1a7 100644
--- a/sysdeps/powerpc/powerpc32/power7/strnlen.S
+++ b/sysdeps/powerpc/powerpc32/power7/strnlen.S
@@ -28,51 +28,47 @@ ENTRY (__strnlen)
 	add	r7,r3,r4      /* Calculate the last acceptable address.  */
 	cmplwi	r4,16
 	li	r0,0	      /* Word with null chars.  */
+	addi	r7,r7,-1
 	ble	L(small_range)
 
-	cmplw	cr7,r3,r7     /* Is the address equal or less than r3?  If
-				 it's equal or less, it means size is either 0
-				 or a negative number.  */
-	ble	cr7,L(proceed)
-
-	li	r7,-1	      /* Make r11 the biggest if r4 <= 0.  */
-L(proceed):
 	rlwinm	r6,r3,3,27,28 /* Calculate padding.  */
 	lwz	r12,0(r8)     /* Load word from memory.  */
 	cmpb	r10,r12,r0    /* Check for null bytes in DWORD1.  */
+#ifdef __LITTLE_ENDIAN__
+	srw	r10,r10,r6
+	slw	r10,r10,r6
+#else
 	slw	r10,r10,r6
 	srw	r10,r10,r6
+#endif
 	cmplwi	cr7,r10,0     /* If r10 == 0, no null's have been found.  */
 	bne	cr7,L(done)
 
-	/* Are we done already?  */
-	addi	r9,r8,4
-	cmplw	cr6,r9,r7
-	bge	cr6,L(end_max)
-
+	clrrwi	r7,r7,2       /* Address of last word.  */
 	mtcrf   0x01,r8
 	/* Are we now aligned to a doubleword boundary?  If so, skip to
 	   the main loop.  Otherwise, go through the alignment code.  */
 
 	bt	29,L(loop_setup)
 
-	/* Handle DWORD2 of pair.  */
+	/* Handle WORD2 of pair.  */
 	lwzu	r12,4(r8)
 	cmpb	r10,r12,r0
 	cmplwi	cr7,r10,0
 	bne	cr7,L(done)
 
-	/* Are we done already?  */
-	addi	r9,r8,4
-	cmplw	cr6,r9,r7
-	bge	cr6,L(end_max)
-
 L(loop_setup):
-	sub	r5,r7,r9
+	/* The last word we want to read in the loop below is the one
+	   containing the last byte of the string, ie. the word at
+	   (s + size - 1) & ~3, or r7.  The first word read is at
+	   r8 + 4, we read 2 * cnt words, so the last word read will
+	   be at r8 + 4 + 8 * cnt - 4.  Solving for cnt gives
+	   cnt = (r7 - r8) / 8  */
+	sub	r5,r7,r8
 	srwi	r6,r5,3	      /* Number of loop iterations.  */
 	mtctr	r6	      /* Setup the counter.  */
-	b	L(loop)
-	/* Main loop to look for the null byte backwards in the string.  Since
+
+	/* Main loop to look for the null byte in the string.  Since
 	   it's a small loop (< 8 instructions), align it to 32-bytes.  */
 	.p2align  5
 L(loop):
@@ -88,15 +84,18 @@ L(loop):
 	cmplwi	cr7,r5,0
 	bne	cr7,L(found)
 	bdnz	L(loop)
-	/* We're here because the counter reached 0, and that means we
-	   didn't have any matches for null in the whole range.  Just return
-	   the original size.  */
-	addi	r9,r8,4
-	cmplw	cr6,r9,r7
-	blt	cr6,L(loop_small)
+
+	/* We may have one more word to read.  */
+	cmplw	cr6,r8,r7
+	beq	cr6,L(end_max)
+
+	lwzu	r12,4(r8)
+	cmpb	r10,r12,r0
+	cmplwi	cr6,r10,0
+	bne	cr6,L(done)
 
 L(end_max):
-	sub	r3,r7,r3
+	mr	r3,r4
 	blr
 
 	/* OK, one (or both) of the words contains a null byte.  Check
@@ -121,49 +120,56 @@ L(found):
 	   We need to make sure the null char is *before* the end of the
 	   range.  */
 L(done):
-	cntlzw	r0,r10	      /* Count leading zeroes before the match.  */
-	srwi	r0,r0,3	      /* Convert leading zeroes to bytes.  */
-	add	r9,r8,r0
-	sub	r6,r9,r3      /* Length until the match.  */
-	cmplw	r9,r7
-	bgt	L(end_max)
-	mr	r3,r6
-	blr
-
-	.align	4
-L(zero):
-	li	r3,0
+#ifdef __LITTLE_ENDIAN__
+	addi	r0,r10,-1
+	andc	r0,r0,r10
+	popcntw	r0,r0
+#else
+	cntlzw	r0,r10	      /* Count leading zeros before the match.  */
+#endif
+	sub	r3,r8,r3
+	srwi	r0,r0,3	      /* Convert leading/trailing zeros to bytes.  */
+	add	r3,r3,r0      /* Length until the match.  */
+	cmplw	r3,r4
+	blelr
+	mr	r3,r4
 	blr
 
-/* Deals with size <= 32.  */
+/* Deals with size <= 16.  */
 	.align	4
 L(small_range):
 	cmplwi	r4,0
-	beq	L(zero)
+	beq	L(end_max)
+
+	clrrwi	r7,r7,2       /* Address of last word.  */
 
 	rlwinm	r6,r3,3,27,28 /* Calculate padding.  */
 	lwz	r12,0(r8)     /* Load word from memory.  */
 	cmpb	r10,r12,r0    /* Check for null bytes in WORD1.  */
+#ifdef __LITTLE_ENDIAN__
+	srw	r10,r10,r6
+	slw	r10,r10,r6
+#else
 	slw	r10,r10,r6
 	srw	r10,r10,r6
+#endif
 	cmplwi	cr7,r10,0
 	bne	cr7,L(done)
 
-	addi    r9,r8,4
-	cmplw	r9,r7
-	bge	L(end_max)
-	b	L(loop_small)
+	cmplw	r8,r7
+	beq	L(end_max)
 
 	.p2align  5
 L(loop_small):
 	lwzu	r12,4(r8)
 	cmpb	r10,r12,r0
-	addi	r9,r8,4
 	cmplwi	cr6,r10,0
 	bne	cr6,L(done)
-	cmplw	r9,r7
-	bge	L(end_max)
-	b	L(loop_small)
+	cmplw	r8,r7
+	bne	L(loop_small)
+	mr	r3,r4
+	blr
+
 END (__strnlen)
 weak_alias (__strnlen, strnlen)
 libc_hidden_builtin_def (strnlen)
diff --git a/sysdeps/powerpc/powerpc64/power7/strnlen.S b/sysdeps/powerpc/powerpc64/power7/strnlen.S
index 37c7dbfe81..51591069df 100644
--- a/sysdeps/powerpc/powerpc64/power7/strnlen.S
+++ b/sysdeps/powerpc/powerpc64/power7/strnlen.S
@@ -24,33 +24,29 @@
 ENTRY (__strnlen)
 	CALL_MCOUNT 2
 	dcbt	0,r3
-	clrrdi  r8,r3,3
+	clrrdi	r8,r3,3
 	add	r7,r3,r4      /* Calculate the last acceptable address.  */
 	cmpldi	r4,32
 	li	r0,0	      /* Doubleword with null chars.  */
+	addi	r7,r7,-1
+
 	/* If we have less than 33 bytes to search, skip to a faster code.  */
 	ble	L(small_range)
 
-	cmpld	cr7,r3,r7    /* Is the address equal or less than r3?  If
-				it's equal or less, it means size is either 0
-				or a negative number.  */
-	ble	cr7,L(proceed)
-
-	li	r7,-1	      /* Make r11 the biggest if r4 <= 0.  */
-L(proceed):
 	rlwinm	r6,r3,3,26,28 /* Calculate padding.  */
 	ld	r12,0(r8)     /* Load doubleword from memory.  */
 	cmpb	r10,r12,r0    /* Check for null bytes in DWORD1.  */
+#ifdef __LITTLE_ENDIAN__
+	srd	r10,r10,r6
+	sld	r10,r10,r6
+#else
 	sld	r10,r10,r6
 	srd	r10,r10,r6
+#endif
 	cmpldi	cr7,r10,0     /* If r10 == 0, no null's have been found.  */
 	bne	cr7,L(done)
 
-	/* Are we done already?  */
-	addi	r9,r8,8
-	cmpld	cr6,r9,r7
-	bge	cr6,L(end_max)
-
+	clrrdi	r7,r7,3       /* Address of last doubleword.  */
 	mtcrf   0x01,r8
 	/* Are we now aligned to a quadword boundary?  If so, skip to
 	   the main loop.  Otherwise, go through the alignment code.  */
@@ -63,17 +59,18 @@ L(proceed):
 	cmpldi	cr7,r10,0
 	bne	cr7,L(done)
 
-	/* Are we done already?  */
-	addi	r9,r8,8
-	cmpld	cr6,r9,r7
-	bge	cr6,L(end_max)
-
 L(loop_setup):
-	sub	r5,r7,r9
+	/* The last dword we want to read in the loop below is the one
+	   containing the last byte of the string, ie. the dword at
+	   (s + size - 1) & ~7, or r7.  The first dword read is at
+	   r8 + 8, we read 2 * cnt dwords, so the last dword read will
+	   be at r8 + 8 + 16 * cnt - 8.  Solving for cnt gives
+	   cnt = (r7 - r8) / 16  */
+	sub	r5,r7,r8
 	srdi	r6,r5,4	      /* Number of loop iterations.  */
 	mtctr	r6	      /* Setup the counter.  */
-	b	L(loop)
-	/* Main loop to look for the null byte backwards in the string.  Since
+
+	/* Main loop to look for the null byte in the string.  Since
 	   it's a small loop (< 8 instructions), align it to 32-bytes.  */
 	.p2align  5
 L(loop):
@@ -89,15 +86,18 @@ L(loop):
 	cmpldi	cr7,r5,0
 	bne	cr7,L(found)
 	bdnz	L(loop)
-	/* We're here because the counter reached 0, and that means we
-	   didn't have any matches for null in the whole range.  Just return
-	   the original size.  */
-	addi	r9,r8,8
-	cmpld	cr6,r9,r7
-	blt	cr6,L(loop_small)
+
+	/* We may have one more dword to read.  */
+	cmpld	cr6,r8,r7
+	beq	cr6,L(end_max)
+
+	ldu	r12,8(r8)
+	cmpb	r10,r12,r0
+	cmpldi	cr6,r10,0
+	bne	cr6,L(done)
 
 L(end_max):
-	sub	r3,r7,r3
+	mr	r3,r4
 	blr
 
 	/* OK, one (or both) of the doublewords contains a null byte.  Check
@@ -119,52 +119,59 @@ L(found):
 	/* r10 has the output of the cmpb instruction, that is, it contains
 	   0xff in the same position as the null byte in the original
 	   doubleword from the string.  Use that to calculate the length.
-	   We need to make sure the null char is *before* the start of the
-	   range (since we're going backwards).  */
+	   We need to make sure the null char is *before* the end of the
+	   range.  */
 L(done):
-	cntlzd	r0,r10	      /* Count leading zeroes before the match.  */
-	srdi	r0,r0,3	      /* Convert leading zeroes to bytes.  */
-	add	r9,r8,r0
-	sub	r6,r9,r3      /* Length until the match.  */
-	cmpld	r9,r7
-	bgt	L(end_max)
-	mr	r3,r6
-	blr
-
-	.align	4
-L(zero):
-	li	r3,0
+#ifdef __LITTLE_ENDIAN__
+	addi	r0,r10,-1
+	andc	r0,r0,r10
+	popcntd	r0,r0
+#else
+	cntlzd	r0,r10	      /* Count leading zeros before the match.  */
+#endif
+	sub	r3,r8,r3
+	srdi	r0,r0,3	      /* Convert leading/trailing zeros to bytes.  */
+	add	r3,r3,r0      /* Length until the match.  */
+	cmpld	r3,r4
+	blelr
+	mr	r3,r4
 	blr
 
 /* Deals with size <= 32.  */
 	.align	4
 L(small_range):
 	cmpldi	r4,0
-	beq	L(zero)
+	beq	L(end_max)
+
+	clrrdi	r7,r7,3       /* Address of last doubleword.  */
 
 	rlwinm	r6,r3,3,26,28 /* Calculate padding.  */
-	ld	r12,0(r8)     /* Load word from memory.  */
+	ld	r12,0(r8)     /* Load doubleword from memory.  */
 	cmpb	r10,r12,r0    /* Check for null bytes in DWORD1.  */
+#ifdef __LITTLE_ENDIAN__
+	srd	r10,r10,r6
+	sld	r10,r10,r6
+#else
 	sld	r10,r10,r6
 	srd	r10,r10,r6
+#endif
 	cmpldi	cr7,r10,0
 	bne	cr7,L(done)
 
-	addi    r9,r8,8
-	cmpld	r9,r7
-	bge	L(end_max)
-	b	L(loop_small)
+	cmpld	r8,r7
+	beq	L(end_max)
 
 	.p2align  5
 L(loop_small):
 	ldu	r12,8(r8)
 	cmpb	r10,r12,r0
-	addi	r9,r8,8
 	cmpldi	cr6,r10,0
 	bne	cr6,L(done)
-	cmpld	r9,r7
-	bge	L(end_max)
-	b	L(loop_small)
+	cmpld	r8,r7
+	bne	L(loop_small)
+	mr	r3,r4
+	blr
+
 END (__strnlen)
 weak_alias (__strnlen, strnlen)
 libc_hidden_builtin_def (strnlen)