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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