strncpy.S

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * arch/alpha/lib/strncpy.S
 * Contributed by Richard Henderson ([email protected])
 *
 * Copy no more than COUNT bytes of the null-terminated string from
 * SRC to DST.  If SRC does not cover all of COUNT, the balance is
 * zeroed.
 *
 * Or, rather, if the kernel cared about that weird ANSI quirk.  This
 * version has cropped that bit o' nastiness as well as assuming that
 * __stxncpy is in range of a branch.
 */
#include <linux/export.h>
	.set noat
	.set noreorder

	.text

	.align 4
	.globl strncpy
	.ent strncpy
strncpy:
	.frame $30, 0, $26
	.prologue 0

	mov	$16, $0		# set return value now
	beq	$18, $zerolen
	unop
	bsr	$23, __stxncpy	# do the work of the copy

	unop
	bne	$18, $multiword	# do we have full words left?
	subq	$24, 1, $3	# nope
	subq	$27, 1, $4

	or	$3, $24, $3	# clear the bits between the last
	or	$4, $27, $4	# written byte and the last byte in COUNT
	andnot	$3, $4, $4
	zap	$1, $4, $1

	stq_u	$1, 0($16)
	ret

	.align	4
$multiword:
	subq	$27, 1, $2	# clear the final bits in the prev word
	or	$2, $27, $2
	zapnot	$1, $2, $1
	subq	$18, 1, $18

	stq_u	$1, 0($16)
	addq	$16, 8, $16
	unop
	beq	$18, 1f

	nop
	unop
	nop
	blbc	$18, 0f

	stq_u	$31, 0($16)	# zero one word
	subq	$18, 1, $18
	addq	$16, 8, $16
	beq	$18, 1f

0:	stq_u	$31, 0($16)	# zero two words
	subq	$18, 2, $18
	stq_u	$31, 8($16)
	addq	$16, 16, $16
	bne	$18, 0b

1:	ldq_u	$1, 0($16)	# clear the leading bits in the final word
	subq	$24, 1, $2
	or	$2, $24, $2

	zap	$1, $2, $1
	stq_u	$1, 0($16)
$zerolen:
	ret

	.end	strncpy
	EXPORT_SYMBOL(strncpy)