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/*
* mpvecdigmulsub(mpdigit *b, int n, mpdigit m, mpdigit *p)
*
* p -= b*m
*
* each step look like:
* hi,lo = m*b[i]
* lo += oldhi + carry
* hi += carry
* p[i] += lo
* oldhi = hi
*
* the registers are:
* hi = DX - constrained by hardware
* lo = AX - constrained by hardware
* b = SI - can't be BP
* p = DI - can't be BP
* i = BP
* n = CX - constrained by LOOP instr
* m = BX
* oldhi = R8
*
*/
TEXT mpvecdigmulsub(SB),$0
MOVQ RARG,SI
MOVL n+8(FP),CX
MOVL m+16(FP),BX
MOVQ p+24(FP),DI
XORL BP,BP
MOVL BP,R8
_mulsubloop:
MOVL (SI)(BP*4),AX /* lo = b[i] */
MULL BX /* hi, lo = b[i] * m */
ADDL R8,AX /* lo += oldhi */
ADCL $0, DX /* hi += carry */
SUBL AX,(DI)(BP*4)
ADCL $0, DX /* hi += carry */
MOVL DX,R8
INCL BP
LOOP _mulsubloop
MOVL CX, AX
SUBL R8,(DI)(BP*4)
SBBQ CX, AX
ORQ $1, AX
RET
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