path: root/sysdeps/alpha/stxncpy.S

/* Copyright (C) 1996-2025 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library.  If not, see
   <https://www.gnu.org/licenses/>.  */

/* Copy no more than COUNT bytes of the null-terminated string from
   SRC to DST.

   This is an internal routine used by strncpy, stpncpy, and strncat.
   As such, it uses special linkage conventions to make implementation
   of these public functions more efficient.

   On input:
	t9 = return address
	a0 = DST
	a1 = SRC
	a2 = COUNT

   Furthermore, COUNT may not be zero.

   On output:
	t0  = last word written
	t8  = bitmask (with one bit set) indicating the last byte written
	t10 = bitmask (with one bit set) indicating the byte position of
	      the end of the range specified by COUNT
	a0  = unaligned address of the last *word* written
	a2  = the number of full words left in COUNT

   Furthermore, v0, a3-a5, t11, and t12 are untouched.
*/


/* This is generally scheduled for the EV5, but should still be pretty
   good for the EV4 too.  */

#include <sysdep.h>

	.set noat
	.set noreorder

	.text
	.type	__stxncpy, @function
	.globl	__stxncpy
	.usepv	__stxncpy, no

	cfi_startproc
	cfi_return_column (t9)

	/* On entry to this basic block:
	   t0 == the first destination word for masking back in
	   t1 == the first source word.  */
	.align 3
stxncpy_aligned:
	/* Create the 1st output word and detect 0's in the 1st input word.  */
	lda	t2, -1		# e1    : build a mask against false zero
	mskqh	t2, a1, t2	# e0    :   detection in the src word
	mskqh	t1, a1, t3	# e0    :
	ornot	t1, t2, t2	# .. e1 :
	mskql	t0, a1, t0	# e0    : assemble the first output word
	cmpbge	zero, t2, t7	# .. e1 : bits set iff null found
	or	t0, t3, t0	# e0    :
	beq	a2, $a_eoc	# .. e1 :
	bne	t7, $a_eos	# .. e1 :

	/* On entry to this basic block:
	   t0 == a source word not containing a null.  */
$a_loop:
	stq_u	t0, 0(a0)	# e0    :
	addq	a0, 8, a0	# .. e1 :
	ldq_u	t0, 0(a1)	# e0    :
	addq	a1, 8, a1	# .. e1 :
	subq	a2, 1, a2	# e0    :
	cmpbge	zero, t0, t7	# .. e1 (stall)
	beq	a2, $a_eoc      # e1    :
	beq	t7, $a_loop	# e1    :

	/* Take care of the final (partial) word store.  At this point
	   the end-of-count bit is set in t7 iff it applies.

	   On entry to this basic block we have:
	   t0 == the source word containing the null
	   t7 == the cmpbge mask that found it.  */
$a_eos:
	negq	t7, t8		# e0    : find low bit set
	and	t7, t8, t8	# e1 (stall)

	/* For the sake of the cache, don't read a destination word
	   if we're not going to need it.  */
	and	t8, 0x80, t6	# e0    :
	bne	t6, 1f		# .. e1 (zdb)

	/* We're doing a partial word store and so need to combine
	   our source and original destination words.  */
	ldq_u	t1, 0(a0)	# e0    :
	subq	t8, 1, t6	# .. e1 :
	or	t8, t6, t7	# e0    :
	unop			#
	zapnot	t0, t7, t0	# e0    : clear src bytes > null
	zap	t1, t7, t1	# .. e1 : clear dst bytes <= null
	or	t0, t1, t0	# e1    :

1:	stq_u	t0, 0(a0)	# e0    :
	ret	(t9)		# e1    :

	/* Add the end-of-count bit to the eos detection bitmask.  */
$a_eoc:
	or	t10, t7, t7
	br	$a_eos

	.align 3
__stxncpy:
	/* Are source and destination co-aligned?  */
	lda	t2, -1
	xor	a0, a1, t1
	srl