patch-1.3.11 linux/arch/alpha/lib/strlen.S

• Lines: 58
• Date: Mon Jul 17 08:50:12 1995
• Orig file: v1.3.10/linux/arch/alpha/lib/strlen.S
• Orig date: Thu Jan 1 02:00:00 1970

diff -u --recursive --new-file v1.3.10/linux/arch/alpha/lib/strlen.S linux/arch/alpha/lib/strlen.S
@@ -0,0 +1,57 @@
+/*
+ * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
+ *
+ * Finds length of a 0-terminated string.  Optimized for the
+ * Alpha architecture:
+ *
+ *	- memory accessed as aligned quadwords only
+ *	- uses bcmpge to compare 8 bytes in parallel
+ *	- does binary search to find 0 byte in last
+ *	  quadword (HAKMEM needed 12 instructions to
+ *	  do this instead of the 9 instructions that
+ *	  binary search needs).
+ */
+
+	.set noreorder
+	.set noat
+
+	.align 3
+
+	.globl	strlen
+	.ent	strlen
+
+strlen:
+	ldq_u	$1, 0($16)	# load first quadword ($16  may be misaligned)
+	lda	$2, -1($31)
+	insqh	$2, $16, $2
+	andnot	$16, 7, $0
+	or	$2, $1, $1
+	cmpbge	$31, $1, $2	# $2  <- bitmask: bit i == 1 <==> i-th byte == 0
+	bne	$2, found
+
+loop:	ldq	$1, 8($0)
+	addq	$0, 8, $0	# addr += 8
+	nop			# helps dual issue last two insns
+	cmpbge	$31, $1, $2
+	beq	$2, loop
+
+found:	blbs	$2, done	# make aligned case fast
+	negq	$2, $3
+	and	$2, $3, $2
+
+	and	$2, 0x0f, $1
+	addq	$0, 4, $3
+	cmoveq	$1, $3, $0
+
+	and	$2, 0x33, $1
+	addq	$0, 2, $3
+	cmoveq	$1, $3, $0
+
+	and	$2, 0x55, $1
+	addq	$0, 1, $3
+	cmoveq	$1, $3, $0
+
+done:	subq	$0, $16, $0
+	ret	$31, ($26)
+
+	.end	strlen