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/*
* A fast checksum routine using movem
* Copyright (c) 1998-2007 Axis Communications AB
*
* csum_partial(const unsigned char * buff, int len, unsigned int sum)
*/
.globl csum_partial
csum_partial:
;; r10 - src
;; r11 - length
;; r12 - checksum
;; Optimized for large packets
subq 10*4, $r11
blt _word_loop
move.d $r11, $acr
subq 9*4,$sp
clearf c
movem $r8,[$sp]
;; do a movem checksum
_mloop: movem [$r10+],$r9 ; read 10 longwords
;; Loop count without touching the c flag.
addoq -10*4, $acr, $acr
;; perform dword checksumming on the 10 longwords
addc $r0,$r12
addc $r1,$r12
addc $r2,$r12
addc $r3,$r12
addc $r4,$r12
addc $r5,$r12
addc $r6,$r12
addc $r7,$r12
addc $r8,$r12
addc $r9,$r12
;; test $acr without trashing carry.
move.d $acr, $acr
bpl _mloop
;; r11 <= acr is not really needed in the mloop, just using the dslot
;; to prepare for what is needed after mloop.
move.d $acr, $r11
;; fold the last carry into r13
addc 0, $r12
movem [$sp+],$r8 ; restore regs
_word_loop:
addq 10*4,$r11 ; compensate for last loop underflowing length
moveq -1,$r9 ; put 0xffff in r9, faster than move.d 0xffff,r9
lsrq 16,$r9
move.d $r12,$r13
lsrq 16,$r13 ; r13 = checksum >> 16
and.d $r9,$r12 ; checksum = checksum & 0xffff
_no_fold:
subq 2,$r11
blt _no_words
add.d $r13,$r12 ; checksum += r13
;; checksum the rest of the words
_wloop: subq 2,$r11
bge _wloop
addu.w [$r10+],$r12
_no_words:
addq 2,$r11
;; see if we have one odd byte more
bne _do_byte
nop
ret
move.d $r12,$r10
_do_byte:
;; copy and checksum the last byte
addu.b [$r10],$r12
ret
move.d $r12,$r10
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