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/* mpvecadd(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *sum) */
/* sum[0:alen] = a[0:alen-1] + b[0:blen-1] */
/* prereq: alen >= blen, sum has room for alen+1 digits */
/* (very old gnu assembler doesn't allow multiline comments) */
.text
.p2align 2,0x90
.globl mpvecadd
mpvecadd:
/* Prelude */
pushl %ebp /* save on stack */
pushl %ebx
pushl %esi
pushl %edi
leal 20(%esp), %ebp /* %ebp = FP for now */
movl 4(%ebp), %edx /* alen */
movl 12(%ebp), %ecx /* blen */
movl 0(%ebp), %esi /* a */
movl 8(%ebp), %ebx /* b */
subl %ecx, %edx
movl 16(%ebp), %edi /* sum */
xorl %ebp, %ebp /* this also sets carry to 0 */
/* skip addition if b is zero */
testl %ecx,%ecx
je _add1
/* sum[0:blen-1],carry = a[0:blen-1] + b[0:blen-1] */
_addloop1:
movl (%esi, %ebp, 4), %eax
adcl (%ebx, %ebp, 4), %eax
movl %eax, (%edi, %ebp, 4)
incl %ebp
loop _addloop1
_add1:
/* jump if alen > blen */
incl %edx
movl %edx, %ecx
loop _addloop2
/* sum[alen] = carry */
_addend:
jb _addcarry
movl $0, (%edi, %ebp, 4)
jmp done
_addcarry:
movl $1, (%edi, %ebp, 4)
jmp done
/* sum[blen:alen-1],carry = a[blen:alen-1] + 0 */
_addloop2:
movl (%esi, %ebp, 4),%eax
adcl $0, %eax
movl %eax, (%edi, %ebp, 4)
incl %ebp
loop _addloop2
jmp _addend
done:
/* Postlude */
popl %edi
popl %esi
popl %ebx
popl %ebp
ret
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