1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * arch/alpha/lib/ev67-strncat.S
4  * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
5  *
6  * Append no more than COUNT characters from the null-terminated string SRC
7  * to the null-terminated string DST.  Always null-terminate the new DST.
8  *
9  * This differs slightly from the semantics in libc in that we never write
10  * past count, whereas libc may write to count+1.  This follows the generic
11  * implementation in lib/string.c and is, IMHO, more sensible.
12  *
13  * Much of the information about 21264 scheduling/coding comes from:
14  *	Compiler Writer's Guide for the Alpha 21264
15  *	abbreviated as 'CWG' in other comments here
16  *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
17  * Scheduling notation:
18  *	E	- either cluster
19  *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1
20  *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1
21  * Try not to change the actual algorithm if possible for consistency.
22  */
23 
24 #include <asm/export.h>
25 	.text
26 
27 	.align 4
28 	.globl strncat
29 	.ent strncat
30 strncat:
31 	.frame $30, 0, $26
32 	.prologue 0
33 
34 	mov	$16, $0		# set up return value
35 	beq	$18, $zerocount	# U :
36 	/* Find the end of the string.  */
37 	ldq_u   $1, 0($16)	# L : load first quadword ($16 may be misaligned)
38 	lda     $2, -1($31)	# E :
39 
40 	insqh   $2, $0, $2	# U :
41 	andnot  $16, 7, $16	# E :
42 	nop			# E :
43 	or      $2, $1, $1	# E :
44 
45 	nop			# E :
46 	nop			# E :
47 	cmpbge  $31, $1, $2	# E : bits set iff byte == 0
48 	bne     $2, $found	# U :
49 
50 $loop:	ldq     $1, 8($16)	# L :
51 	addq    $16, 8, $16	# E :
52 	cmpbge  $31, $1, $2	# E :
53 	beq     $2, $loop	# U :
54 
55 $found:	cttz	$2, $3		# U0 :
56 	addq	$16, $3, $16	# E :
57 	nop			# E :
58 	bsr	$23, __stxncpy	# L0 :/* Now do the append.  */
59 
60 	/* Worry about the null termination.  */
61 
62 	zapnot	$1, $27, $2	# U : was last byte a null?
63 	cmplt	$27, $24, $5	# E : did we fill the buffer completely?
64 	bne	$2, 0f		# U :
65 	ret			# L0 :
66 
67 0:	or	$5, $18, $2	# E :
68 	nop
69 	bne	$2, 2f		# U :
70 	and	$24, 0x80, $3	# E : no zero next byte
71 
72 	nop			# E :
73 	bne	$3, 1f		# U :
74 	/* Here there are bytes left in the current word.  Clear one.  */
75 	addq	$24, $24, $24	# E : end-of-count bit <<= 1
76 	nop			# E :
77 
78 2:	zap	$1, $24, $1	# U :
79 	nop			# E :
80 	stq_u	$1, 0($16)	# L :
81 	ret			# L0 :
82 
83 1:	/* Here we must clear the first byte of the next DST word */
84 	stb	$31, 8($16)	# L :
85 	nop			# E :
86 	nop			# E :
87 	ret			# L0 :
88 
89 $zerocount:
90 	nop			# E :
91 	nop			# E :
92 	nop			# E :
93 	ret			# L0 :
94 
95 	.end strncat
96 	EXPORT_SYMBOL(strncat)
97