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/arch/cris/arch-v10/lib/checksum.S

https://bitbucket.org/evzijst/gittest
Assembly | 124 lines | 75 code | 29 blank | 20 comment | 0 complexity | d72274f14601db99f411061f07ff4fb2 MD5 | raw file
  1/* $Id: checksum.S,v 1.1 2001/12/17 13:59:27 bjornw Exp $
  2 * A fast checksum routine using movem
  3 * Copyright (c) 1998-2001 Axis Communications AB
  4 *
  5 * csum_partial(const unsigned char * buff, int len, unsigned int sum)
  6 */
  7
  8	.globl	csum_partial
  9csum_partial:
 10	
 11	;; r10 - src
 12	;; r11 - length
 13	;; r12 - checksum
 14
 15	;; check for breakeven length between movem and normal word looping versions
 16	;; we also do _NOT_ want to compute a checksum over more than the 
 17	;; actual length when length < 40
 18	
 19	cmpu.w	80,$r11
 20	blo	_word_loop
 21	nop
 22
 23	;; need to save the registers we use below in the movem loop
 24	;; this overhead is why we have a check above for breakeven length
 25	;; only r0 - r8 have to be saved, the other ones are clobber-able
 26	;; according to the ABI
 27	
 28	subq	9*4,$sp
 29	movem	$r8,[$sp]
 30	
 31	;; do a movem checksum
 32
 33	subq	10*4,$r11	; update length for the first loop
 34	
 35_mloop:	movem	[$r10+],$r9	; read 10 longwords
 36
 37	;; perform dword checksumming on the 10 longwords
 38	
 39	add.d	$r0,$r12
 40	ax
 41	add.d	$r1,$r12
 42	ax
 43	add.d	$r2,$r12
 44	ax
 45	add.d	$r3,$r12
 46	ax
 47	add.d	$r4,$r12
 48	ax
 49	add.d	$r5,$r12
 50	ax
 51	add.d	$r6,$r12
 52	ax
 53	add.d	$r7,$r12
 54	ax
 55	add.d	$r8,$r12
 56	ax
 57	add.d	$r9,$r12
 58
 59	;; fold the carry into the checksum, to avoid having to loop the carry
 60	;; back into the top
 61	
 62	ax
 63	addq	0,$r12
 64	ax			; do it again, since we might have generated a carry
 65	addq	0,$r12
 66
 67	subq	10*4,$r11
 68	bge	_mloop
 69	nop
 70
 71	addq	10*4,$r11	; compensate for last loop underflowing length
 72
 73	movem	[$sp+],$r8	; restore regs
 74
 75_word_loop:
 76	;; only fold if there is anything to fold.
 77
 78	cmpq	0,$r12
 79	beq	_no_fold
 80
 81	;; fold 32-bit checksum into a 16-bit checksum, to avoid carries below.
 82	;; r9 and r13 can be used as temporaries.
 83	
 84	moveq	-1,$r9		; put 0xffff in r9, faster than move.d 0xffff,r9
 85	lsrq	16,$r9
 86	
 87	move.d	$r12,$r13
 88	lsrq	16,$r13		; r13 = checksum >> 16
 89	and.d	$r9,$r12		; checksum = checksum & 0xffff
 90	add.d	$r13,$r12		; checksum += r13
 91	move.d	$r12,$r13		; do the same again, maybe we got a carry last add
 92	lsrq	16,$r13
 93	and.d	$r9,$r12
 94	add.d	$r13,$r12
 95
 96_no_fold:
 97	cmpq	2,$r11
 98	blt	_no_words
 99	nop
100	
101	;; checksum the rest of the words
102	
103	subq	2,$r11
104	
105_wloop:	subq	2,$r11
106	bge	_wloop
107	addu.w	[$r10+],$r12
108	
109	addq	2,$r11
110		
111_no_words:
112	;; see if we have one odd byte more
113	cmpq	1,$r11
114	beq	_do_byte
115	nop
116	ret
117	move.d	$r12, $r10
118
119_do_byte:	
120	;; copy and checksum the last byte
121	addu.b	[$r10],$r12
122	ret
123	move.d	$r12, $r10
124