Dmitry Olshansky:
> Probably, this could be a starting point (BTW In D you can write
> templates very easy):
>
> T dot_product(size_t N, T)(T[] a, T[] b){
> static if (N == 1){
> return a[0] * b[0];
> }else{
> return a[0] * b[0] + dot_product!(N-1)(a[1..$],b[1..$]);
> }
> }
>
> void main()
> {
> int[] a = [1, 2, 3];
> int[] b = [5, 6, 7];
> assert( dot_product!3(a,b) == 38 );//sanity check
> }
> And I didn't checked the disassembly.
I have added another version:
import std.typetuple: TypeTuple;
T dot_product(size_t N, T)(T[] a, T[] b) {
static if (N == 1)
return a[0] * b[0];
else
return a[0] * b[0] + dot_product!(N-1)(a[1..$],b[1..$]);
}
template Iota(int stop) {
static if (stop <= 0)
alias TypeTuple!() Iota;
else
alias TypeTuple!(Iota!(stop-1), stop-1) Iota;
}
T dotProduct(T, int N)(T[N] a, T[N] b) {
T result = 0;
foreach (i; Iota!(N))
result += a[i] * b[i];
return result;
}
void main() {
double[3] a = [1., 2., 3.];
double[3] b = [5., 6., 7.];
assert(dot_product!3(a, b) == 38.0);
assert(dotProduct(a, b) == 38.0);
}
The asm (dmd 2.047 -O -release -inline):
_D6test6b22__T11dot_productVi3TdZ11dot_productFAdAdZd comdat
sub ESP,038h
mov EDX,048h[ESP]
mov EAX,044h[ESP]
push EBX
mov ECX,044h[ESP]
mov EBX,048h[ESP]
push ESI
dec EBX
mov ESI,044h[ESP]
mov 8[ESP],EBX
dec ESI
mov EAX,044h[ESP]
mov 010h[ESP],ESI
mov EAX,8[ESP]
mov EBX,010h[ESP]
dec EBX
dec EAX
fld qword ptr [EDX]
lea EDX,8[EDX]
fmul qword ptr [ECX]
lea ECX,8[ECX]
mov 0Ch[ESP],EDX
mov 014h[ESP],ECX
fld qword ptr [EDX]
lea EDX,8[EDX]
fmul qword ptr [ECX]
lea ECX,8[ECX]
fld qword ptr [EDX]
fmul qword ptr [ECX]
faddp ST(1),ST
faddp ST(1),ST
pop ESI
pop EBX
add ESP,038h
ret 010h
_D6test6b22__T11dot_productVk2TdZ11dot_productFAdAdZd comdat
sub ESP,018h
mov EDX,028h[ESP]
mov EAX,024h[ESP]
push EBX
mov ECX,024h[ESP]
mov EBX,028h[ESP]
push ESI
mov ESI,024h[ESP]
mov EAX,024h[ESP]
dec ESI
dec EBX
fld qword ptr [EDX]
lea EDX,8[EDX]
fmul qword ptr [ECX]
lea ECX,8[ECX]
fld qword ptr [EDX]
fmul qword ptr [ECX]
faddp ST(1),ST
pop ESI
pop EBX
add ESP,018h
ret 010h
_D6test6b22__T11dot_productVk1TdZ11dot_productFAdAdZd comdat
mov EDX,010h[ESP]
mov EAX,0Ch[ESP]
mov EAX,4[ESP]
fld qword ptr [EDX]
mov EDX,8[ESP]
fmul qword ptr [EDX]
ret 010h
_D6test6b21__T10dotProductTdVk3Z10dotProductFG3dG3dZd comdat
sub ESP,048h
fld qword ptr 064h[ESP]
fmul qword ptr 04Ch[ESP]
fldz
faddp ST(1),ST
fstp qword ptr [ESP]
fld qword ptr 06Ch[ESP]
fld qword ptr 074h[ESP]
fxch ST1
fmul qword ptr 054h[ESP]
fxch ST1
fmul qword ptr 05Ch[ESP]
faddp ST(1),ST
fadd qword ptr [ESP]
fstp qword ptr [ESP]
fld qword ptr [ESP]
add ESP,048h
ret 030h
Bye,
bearophile
