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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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