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* A fast checksum+copy routine using movem
* Copyright (c) 1998, 2001, 2003 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
;; 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,$r12
blo _word_loop
;; need to save the registers we use below in the movem loop
;; this overhead is why we have a check above for breakeven length
;; only r0 - r8 have to be saved, the other ones are clobber-able
;; according to the ABI
subq 9*4,$sp
subq 10*4,$r12 ; update length for the first loop
movem $r8,[$sp]
;; do a movem copy and checksum
1: ;; A failing userspace access (the read) will have this as PC.
_mloop: movem [$r10+],$r9 ; read 10 longwords
movem $r9,[$r11+] ; write 10 longwords
;; perform dword checksumming on the 10 longwords
add.d $r0,$r13
addc $r1,$r13
addc $r2,$r13
addc $r3,$r13
addc $r4,$r13
addc $r5,$r13
addc $r6,$r13
addc $r7,$r13
addc $r8,$r13
addc $r9,$r13
;; fold the carry into the checksum, to avoid having to loop the carry
;; back into the top
addc 0,$r13
addc 0,$r13 ; do it again, since we might have generated a carry
subq 10*4,$r12
bge _mloop
addq 10*4,$r12 ; compensate for last loop underflowing length
movem [$sp+],$r8 ; restore regs
;; 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
cmpq 2,$r12
blt _no_words
;; copy and checksum the rest of the words
subq 2,$r12
2: ;; A failing userspace access for the read below will have this as PC.
_wloop: move.w [$r10+],$r9
addu.w $r9,$r13
subq 2,$r12
bge _wloop
move.w $r9,[$r11+]
addq 2,$r12
;; see if we have one odd byte more
cmpq 1,$r12
beq _do_byte
move.d $r13,$r10
;; copy and checksum the last byte
3: ;; A failing userspace access for the read below will have this as PC.
move.b [$r10],$r9
addu.b $r9,$r13
move.b $r9,[$r11]
move.d $r13,$r10