1/*
2 * A fast checksum+copy routine using movem
3 * Copyright (c) 1998, 2001, 2003 Axis Communications AB
4 *
5 * Authors:	Bjorn Wesen
6 *
7 * csum_partial_copy_nocheck(const char *src, char *dst,
8 *		             int len, unsigned int sum)
9 */
10
11	.globl	csum_partial_copy_nocheck
12csum_partial_copy_nocheck:
13
14	;; r10 - src
15	;; r11 - dst
16	;; r12 - length
17	;; r13 - checksum
18
19	;; check for breakeven length between movem and normal word looping versions
20	;; we also do _NOT_ want to compute a checksum over more than the
21	;; actual length when length < 40
22
23	cmpu.w	80,$r12
24	blo	_word_loop
25	nop
26
27	;; need to save the registers we use below in the movem loop
28	;; this overhead is why we have a check above for breakeven length
29	;; only r0 - r8 have to be saved, the other ones are clobber-able
30	;; according to the ABI
31
32	subq	9*4,$sp
33	subq	10*4,$r12	; update length for the first loop
34	movem	$r8,[$sp]
35
36	;; do a movem copy and checksum
37
381:	;; A failing userspace access (the read) will have this as PC.
39_mloop:	movem	[$r10+],$r9	; read 10 longwords
40	movem	$r9,[$r11+]	; write 10 longwords
41
42	;; perform dword checksumming on the 10 longwords
43
44	add.d	$r0,$r13
45	addc	$r1,$r13
46	addc	$r2,$r13
47	addc	$r3,$r13
48	addc	$r4,$r13
49	addc	$r5,$r13
50	addc	$r6,$r13
51	addc	$r7,$r13
52	addc	$r8,$r13
53	addc	$r9,$r13
54
55	;; fold the carry into the checksum, to avoid having to loop the carry
56	;; back into the top
57
58	addc	0,$r13
59	addc	0,$r13		; do it again, since we might have generated a carry
60
61	subq	10*4,$r12
62	bge	_mloop
63	nop
64
65	addq	10*4,$r12	; compensate for last loop underflowing length
66
67	movem	[$sp+],$r8	; restore regs
68
69_word_loop:
70	;; only fold if there is anything to fold.
71
72	cmpq	0,$r13
73	beq	_no_fold
74
75	;; fold 32-bit checksum into a 16-bit checksum, to avoid carries below
76	;; r9 can be used as temporary.
77
78	move.d	$r13,$r9
79	lsrq	16,$r9		; r0 = checksum >> 16
80	and.d	0xffff,$r13	; checksum = checksum & 0xffff
81	add.d	$r9,$r13	; checksum += r0
82	move.d	$r13,$r9	; do the same again, maybe we got a carry last add
83	lsrq	16,$r9
84	and.d	0xffff,$r13
85	add.d	$r9,$r13
86
87_no_fold:
88	cmpq	2,$r12
89	blt	_no_words
90	nop
91
92	;; copy and checksum the rest of the words
93
94	subq	2,$r12
95
962:	;; A failing userspace access for the read below will have this as PC.
97_wloop:	move.w	[$r10+],$r9
98	addu.w	$r9,$r13
99	subq	2,$r12
100	bge	_wloop
101	move.w	$r9,[$r11+]
102
103	addq	2,$r12
104
105_no_words:
106	;; see if we have one odd byte more
107	cmpq	1,$r12
108	beq	_do_byte
109	nop
110	ret
111	move.d	$r13,$r10
112
113_do_byte:
114	;; copy and checksum the last byte
1153:	;; A failing userspace access for the read below will have this as PC.
116	move.b	[$r10],$r9
117	addu.b	$r9,$r13
118	move.b	$r9,[$r11]
119	ret
120	move.d	$r13,$r10
121