arch/alpha/lib/strlen.S

Source file repositories/reference/linux-study-clean/arch/alpha/lib/strlen.S

File Facts

System
Linux kernel
Corpus path
arch/alpha/lib/strlen.S
Extension
.S
Size
1222 bytes
Lines
60
Domain
Architecture Layer
Bucket
arch/alpha
Inferred role
Architecture Layer: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

#include <linux/export.h>
	.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
	EXPORT_SYMBOL(strlen)

Annotation

Implementation Notes