# | |
# mpvecdigmul(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+n = SI - can't be BP | |
# p+n = DI - can't be BP | |
# i-n = BP | |
# m = BX | |
# oldhi = CX | |
# | |
.text | |
.p2align 2,0x90 | |
.globl mpvecdigmuladd | |
mpvecdigmuladd: | |
# 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 | |
movl %ecx, %ebp | |
negl %ebp # BP = -n | |
shll $2, %ecx | |
addl %ecx, %esi # SI = b + n | |
addl %ecx, %edi # DI = p + n | |
xorl %ecx, %ecx | |
_muladdloop: | |
movl (%esi, %ebp, 4), %eax # lo = b[i] | |
mull %ebx # hi, lo = b[i] * m | |
addl %ecx,%eax # lo += oldhi | |
jae _muladdnocarry1 | |
incl %edx # hi += carry | |
_muladdnocarry1: | |
addl %eax, (%edi, %ebp, 4) # p[i] += lo | |
jae _muladdnocarry2 | |
incl %edx # hi += carry | |
_muladdnocarry2: | |
movl %edx, %ecx # oldhi = hi | |
incl %ebp # i++ | |
jnz _muladdloop | |
xorl %eax, %eax | |
addl %ecx, (%edi, %ebp, 4) # p[n] + oldhi | |
adcl %eax, %eax # return carry out of p[n] | |
# Postlude | |
popl %edi | |
popl %esi | |
popl %ebx | |
popl %ebp | |
ret | |