Hello bearophile,
Pelle:
I doubt that gives any performance gains. typeid(a).getHash should be
a constant expression anyway, and I don't see any gains in my tiny
benchmark test.
My code shows a limited time difference:
import std.stdio: writeln;
import std.date: getUTCtime, ticksPerSecond;
void main() {
enum int NLOOP = 30_000_000;
string s = "and I'd like to add a toHash() member, but I can't
find the built-in string hash function.";
{
auto t0 = getUTCtime();
auto stringHash =&(typeid(s).getHash);
hash_t tot;
for (int i; i < NLOOP; i++)
tot += stringHash(&s);
auto t1 = getUTCtime();
writeln(tot, " ", (t1 - t0) / cast(double)ticksPerSecond);
}
{
auto t0 = getUTCtime();
hash_t tot;
for (int i; i < NLOOP; i++)
tot += typeid(s).getHash(&s);
auto t1 = getUTCtime();
writeln(tot, " ", (t1 - t0) / cast(double)ticksPerSecond);
}
}
And the asm shows the first loop to contain one less instruction (dmd
2.048, -O -release -inline), so the difference is small:
L42: lea ECX,01Ch[ESP]
mov EAX,02Ch[ESP]
push ECX
call EDI
add ESI,EAX
inc EBX
cmp EBX,01C9C380h
jb L42
LA7: lea EDX,01Ch[ESP]
mov ECX,_D12TypeInfo_Aya6__initZ
DMD seems to do a bad job of dead assignment removal at the ASM level. I've
seen this befor where half the asm in large blocks was dead.
mov EAX,offset FLAT:_D12TypeInfo_Aya6__initZ
push EDX
call dword ptr 018h[ECX]
add EDI,EAX
inc EBX
cmp EBX,01C9C380h
jb LA7
Bye,
bearophile
--
... <IXOYE><
