Subversion Repositories planix.SVN

#define BDNZ    BC      16,0,
#define BDNE    BC      0,2,

/*
 *      mpvecsub(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *diff)
 *
 *              diff[0:alen-1] = a[0:alen-1] - b[0:blen-1]
 *
 *      prereq: alen >= blen, diff has room for alen digits
 *
 *              R3 == a
 *              R4 == alen
 *              R5 == b
 *              R6 == blen
 *              R7 == diff
 *              R8 == temporary
 *              R9 == temporary
 */
TEXT    mpvecsub(SB),$-4

        MOVW    alen+4(FP),R4
        MOVW    b+8(FP),R5
        MOVW    blen+12(FP),R6
        MOVW    diff+16(FP),R7
        SUB     R6, R4          /* calculate counter for second loop (alen > blen) */
        SUB     $4, R3          /* pre decrement for MOVWU's */
        SUB     $4, R5          /* pre decrement for MOVWU's */
        SUBC    $4, R7          /* pre decrement for MOVWU's and set carry */

        /* skip subraction if b is zero */
        CMP     R0,R6
        BEQ     _sub1

        /* diff[0:blen-1],borrow = a[0:blen-1] - b[0:blen-1] */
        MOVW    R6, CTR
_subloop1:
        MOVWU   4(R3), R8
        MOVWU   4(R5), R9
        SUBE    R9, R8, R8
        MOVWU   R8, 4(R7)
        BDNZ    _subloop1

_sub1:
        /* skip subtraction if a is zero */
        CMP     R0, R4
        BEQ     _subend

        /* diff[blen:alen-1] = a[blen:alen-1] - 0 + carry */
        MOVW    R4, CTR
_subloop2:
        MOVWU   4(R3), R8
        SUBE    R0, R8
        MOVWU   R8, 4(R7)
        BDNZ    _subloop2
_subend:
        RETURN