| /* $Id: checksum.S,v 1.1 2001/12/17 13:59:27 bjornw Exp $ |
| * A fast checksum routine using movem |
| * Copyright (c) 1998-2001 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 |
| |
| ;; 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,$r11 |
| blo _word_loop |
| nop |
| |
| ;; need to save the registers we use below in the movem loop |
| ;; this overhead is why we have a check above for breakeven length |
| ;; only r0 - r8 have to be saved, the other ones are clobber-able |
| ;; according to the ABI |
| |
| subq 9*4,$sp |
| movem $r8,[$sp] |
| |
| ;; do a movem checksum |
| |
| subq 10*4,$r11 ; update length for the first loop |
| |
| _mloop: movem [$r10+],$r9 ; read 10 longwords |
| |
| ;; perform dword checksumming on the 10 longwords |
| |
| add.d $r0,$r12 |
| ax |
| add.d $r1,$r12 |
| ax |
| add.d $r2,$r12 |
| ax |
| add.d $r3,$r12 |
| ax |
| add.d $r4,$r12 |
| ax |
| add.d $r5,$r12 |
| ax |
| add.d $r6,$r12 |
| ax |
| add.d $r7,$r12 |
| ax |
| add.d $r8,$r12 |
| ax |
| add.d $r9,$r12 |
| |
| ;; fold the carry into the checksum, to avoid having to loop the carry |
| ;; back into the top |
| |
| ax |
| addq 0,$r12 |
| ax ; do it again, since we might have generated a carry |
| addq 0,$r12 |
| |
| subq 10*4,$r11 |
| bge _mloop |
| nop |
| |
| addq 10*4,$r11 ; compensate for last loop underflowing length |
| |
| movem [$sp+],$r8 ; restore regs |
| |
| _word_loop: |
| ;; only fold if there is anything to fold. |
| |
| cmpq 0,$r12 |
| beq _no_fold |
| |
| ;; fold 32-bit checksum into a 16-bit checksum, to avoid carries below. |
| ;; r9 and r13 can be used as temporaries. |
| |
| moveq -1,$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 |
| add.d $r13,$r12 ; checksum += r13 |
| move.d $r12,$r13 ; do the same again, maybe we got a carry last add |
| lsrq 16,$r13 |
| and.d $r9,$r12 |
| add.d $r13,$r12 |
| |
| _no_fold: |
| cmpq 2,$r11 |
| blt _no_words |
| nop |
| |
| ;; checksum the rest of the words |
| |
| subq 2,$r11 |
| |
| _wloop: subq 2,$r11 |
| bge _wloop |
| addu.w [$r10+],$r12 |
| |
| addq 2,$r11 |
| |
| _no_words: |
| ;; see if we have one odd byte more |
| cmpq 1,$r11 |
| beq _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 |
| |
