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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 = EX
*
*/
.text
.globl _mpvecdigmulsub
_mpvecdigmulsub:
/* Prelude */
pushl %ebp /* save on stack */
pushl %ebx
pushl %esi
pushl %edi
leal 20(%esp), %ebp /* %ebp = FP for now */
movl 0(%ebp), %esi /* b */
movl 4(%ebp), %ecx /* n */
movl 8(%ebp), %ebx /* m */
movl 12(%ebp), %edi /* p */
xorl %ebp, %ebp
pushl %ebp
1:
movl (%esi, %ebp, 4),%eax /* lo = b[i] */
mull %ebx /* hi, lo = b[i] * m */
addl 0(%esp), %eax /* lo += oldhi */
jae 2f
incl %edx /* hi += carry */
2:
subl %eax, (%edi, %ebp, 4)
jae 3f
incl %edx /* hi += carry */
3:
movl %edx, 0(%esp)
incl %ebp
loop 1b
popl %eax
subl %eax, (%edi, %ebp, 4)
jae 4f
movl $-1, %eax
jmp 5f
4:
movl $1, %eax
5:
/* Postlude */
popl %edi
popl %esi
popl %ebx
popl %ebp
ret
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