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/*
* 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
*/
TEXT mpvecsub(SB),$0
MOVL a+0(FP),SI
MOVL b+8(FP),BX
MOVL alen+4(FP),DX
MOVL blen+12(FP),CX
MOVL diff+16(FP),DI
SUBL CX,DX
XORL BP,BP /* this also sets carry to 0 */
/* skip subraction if b is zero */
TESTL CX,CX
JZ _sub1
/* diff[0:blen-1],borrow = a[0:blen-1] - b[0:blen-1] */
_subloop1:
MOVL (SI)(BP*4),AX
SBBL (BX)(BP*4),AX
MOVL AX,(DI)(BP*4)
INCL BP
LOOP _subloop1
_sub1:
INCL DX
MOVL DX,CX
LOOP _subloop2
RET
/* diff[blen:alen-1] = a[blen:alen-1] - 0 */
_subloop2:
MOVL (SI)(BP*4),AX
SBBL $0,AX
MOVL AX,(DI)(BP*4)
INCL BP
LOOP _subloop2
RET
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