xref: /linux/arch/alpha/lib/ev67-strncat.S (revision 827634added7f38b7d724cab1dccdb2b004c13c3) 
1/*
2 * arch/alpha/lib/ev67-strncat.S
3 * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
4 *
5 * Append no more than COUNT characters from the null-terminated string SRC
6 * to the null-terminated string DST.  Always null-terminate the new DST.
7 *
8 * This differs slightly from the semantics in libc in that we never write
9 * past count, whereas libc may write to count+1.  This follows the generic
10 * implementation in lib/string.c and is, IMHO, more sensible.
11 *
12 * Much of the information about 21264 scheduling/coding comes from:
13 *	Compiler Writer's Guide for the Alpha 21264
14 *	abbreviated as 'CWG' in other comments here
15 *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
16 * Scheduling notation:
17 *	E	- either cluster
18 *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1
19 *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1
20 * Try not to change the actual algorithm if possible for consistency.
21 */
22
23
24	.text
25
26	.align 4
27	.globl strncat
28	.ent strncat
29strncat:
30	.frame $30, 0, $26
31	.prologue 0
32
33	mov	$16, $0		# set up return value
34	beq	$18, $zerocount	# U :
35	/* Find the end of the string.  */
36	ldq_u   $1, 0($16)	# L : load first quadword ($16 may be misaligned)
37	lda     $2, -1($31)	# E :
38
39	insqh   $2, $0, $2	# U :
40	andnot  $16, 7, $16	# E :
41	nop			# E :
42	or      $2, $1, $1	# E :
43
44	nop			# E :
45	nop			# E :
46	cmpbge  $31, $1, $2	# E : bits set iff byte == 0
47	bne     $2, $found	# U :
48
49$loop:	ldq     $1, 8($16)	# L :
50	addq    $16, 8, $16	# E :
51	cmpbge  $31, $1, $2	# E :
52	beq     $2, $loop	# U :
53
54$found:	cttz	$2, $3		# U0 :
55	addq	$16, $3, $16	# E :
56	nop			# E :
57	bsr	$23, __stxncpy	# L0 :/* Now do the append.  */
58
59	/* Worry about the null termination.  */
60
61	zapnot	$1, $27, $2	# U : was last byte a null?
62	cmplt	$27, $24, $5	# E : did we fill the buffer completely?
63	bne	$2, 0f		# U :
64	ret			# L0 :
65
660:	or	$5, $18, $2	# E :
67	nop
68	bne	$2, 2f		# U :
69	and	$24, 0x80, $3	# E : no zero next byte
70
71	nop			# E :
72	bne	$3, 1f		# U :
73	/* Here there are bytes left in the current word.  Clear one.  */
74	addq	$24, $24, $24	# E : end-of-count bit <<= 1
75	nop			# E :
76
772:	zap	$1, $24, $1	# U :
78	nop			# E :
79	stq_u	$1, 0($16)	# L :
80	ret			# L0 :
81
821:	/* Here we must clear the first byte of the next DST word */
83	stb	$31, 8($16)	# L :
84	nop			# E :
85	nop			# E :
86	ret			# L0 :
87
88$zerocount:
89	nop			# E :
90	nop			# E :
91	nop			# E :
92	ret			# L0 :
93
94	.end strncat
95