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/* $Id: checksumcopy.S,v 1.1 2001/12/17 13:59:27 bjornw Exp $
* A fast checksum+copy routine using movem
* Copyright (c) 1998, 2001 Axis Communications AB
*
* Authors: Bjorn Wesen
*
* csum_partial_copy_nocheck(const char *src, char *dst,
* int len, unsigned int sum)
*/
.globl csum_partial_copy_nocheck
csum_partial_copy_nocheck:
;; r10 - src
;; r11 - dst
;; r12 - length
;; r13 - checksum
;; check for breakeven length between movem and normal word looping versions
;; we also do _NOT_ want to compute a checksum over more than the
;; actual length when length < 40
cmpu.w 80, $r12
blo _word_loop
nop
;; need to save the registers we use below in the movem loop
;; this overhead is why we have a check above for breakeven length
;; only r0 - r8 have to be saved, the other ones are clobber-able
;; according to the ABI
subq 9*4, $sp
movem $r8, [$sp]
;; do a movem copy and checksum
subq 10*4, $r12 ; update length for the first loop
_mloop: movem [$r10+],$r9 ; read 10 longwords
1: ;; A failing userspace access will have this as PC.
movem $r9,[$r11+] ; write 10 longwords
;; perform dword checksumming on the 10 longwords
add.d $r0,$r13
ax
add.d $r1,$r13
ax
add.d $r2,$r13
ax
add.d $r3,$r13
ax
add.d $r4,$r13
ax
add.d $r5,$r13
ax
add.d $r6,$r13
ax
add.d $r7,$r13
ax
add.d $r8,$r13
ax
add.d $r9,$r13
;; fold the carry into the checksum, to avoid having to loop the carry
;; back into the top
ax
addq 0,$r13
ax ; do it again, since we might have generated a carry
addq 0,$r13
subq 10*4,$r12
bge _mloop
nop
addq 10*4,$r12 ; compensate for last loop underflowing length
movem [$sp+],$r8 ; restore regs
_word_loop:
;; only fold if there is anything to fold.
cmpq 0,$r13
beq _no_fold
;; fold 32-bit checksum into a 16-bit checksum, to avoid carries below
;; r9 can be used as temporary.
move.d $r13,$r9
lsrq 16,$r9 ; r0 = checksum >> 16
and.d 0xffff,$r13 ; checksum = checksum & 0xffff
add.d $r9,$r13 ; checksum += r0
move.d $r13,$r9 ; do the same again, maybe we got a carry last add
lsrq 16,$r9
and.d 0xffff,$r13
add.d $r9,$r13
_no_fold:
cmpq 2,$r12
blt _no_words
nop
;; copy and checksum the rest of the words
subq 2,$r12
_wloop: move.w [$r10+],$r9
2: ;; A failing userspace access will have this as PC.
addu.w $r9,$r13
subq 2,$r12
bge _wloop
move.w $r9,[$r11+]
addq 2,$r12
_no_words:
;; see if we have one odd byte more
cmpq 1,$r12
beq _do_byte
nop
ret
move.d $r13, $r10
_do_byte:
;; copy and checksum the last byte
move.b [$r10],$r9
3: ;; A failing userspace access will have this as PC.
addu.b $r9,$r13
move.b $r9,[$r11]
ret
move.d $r13, $r10
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