On Thursday, 7 September 2017 at 05:45:58 UTC, Ali Çehreli wrote:
On 09/06/2017 07:06 PM, Psychological Cleanup wrote:
if I have a non-double buffer and temporarily convert to
double then
convert back, do I save many cycles rather than just using a
double
buffer? I know it will bea lot more memory, but I'm
specifically talking
about the cycles in converting to and from vs no conversion.
Using a double for everything gives the highest precision and
makes
things much easier but is that the way to go or does it costs
quite a
bit in performance?
You have to measure. Here's a start:
import std.conv;
import std.range;
import std.datetime;
import std.stdio;
double workWithDouble(double d) {
return d * d / 7;
}
void workWithFloats(float[] floats) {
foreach (ref f; floats) {
f = workWithDouble(f).to!float;
}
}
void workWithDoubles(double[] doubles) {
foreach (ref d; doubles) {
d = workWithDouble(d);
}
}
void main() {
foreach (n; [ 1_000, 1_000_000, 10_000_000 ]) {
const beg = -1f;
const end = 1f;
const step = (end - beg) / n;
auto floats = iota(beg, end, step).array;
auto doubles = iota(double(beg), end, step).array;
{
auto sw = StopWatch(AutoStart.yes);
workWithDoubles(doubles);
writefln("%10s no conversion: %10s usecs", n,
sw.peek().usecs);
}
{
auto sw = StopWatch(AutoStart.yes);
workWithFloats(floats);
writefln("%10s with conversion: %10s usecs", n,
sw.peek().usecs);
}
}
}
Conversion seems to be more costly:
1000 no conversion: 27 usecs
1000 with conversion: 40 usecs
1000000 no conversion: 1715 usecs
1000000 with conversion: 5412 usecs
10000000 no conversion: 16280 usecs
10000000 with conversion: 47190 usecs
Ali
Thanks. my results
dmd x86 debug
asserts on the line `auto floats = iota(beg, end,
step).array;`
dmd x64 debug
1000 no conversion: 15 usecs
1000 with conversion: 5 usecs
1000000 no conversion: 2824 usecs
1000000 with conversion: 5689 usecs
10000000 no conversion: 24148 usecs
10000000 with conversion: 56335 usecs
dmd release x86
1000 no conversion: 1 usecs
1000 with conversion: 1 usecs
1000000 no conversion: 1903 usecs
1000000 with conversion: 1262 usecs
10000000 no conversion: 19156 usecs
10000000 with conversion: 12831 usecs
dmd release x64
1000 no conversion: 4 usecs
1000 with conversion: 17 usecs
1000000 no conversion: 4531 usecs
1000000 with conversion: 4516 usecs
10000000 no conversion: 45928 usecs
10000000 with conversion: 46080 usecs
ldc x86 debug
1000 no conversion: 3 usecs
1000 with conversion: 32 usecs
1000000 no conversion: 3563 usecs
1000000 with conversion: 19240 usecs
10000000 no conversion: 35986 usecs
10000000 with conversion: 192025 usecs
ldc x64 debug
1000 no conversion: 2 usecs
1000 with conversion: 10 usecs
1000000 no conversion: 2855 usecs
1000000 with conversion: 10309 usecs
10000000 no conversion: 28254 usecs
10000000 with conversion: 101380 usecs
ldc x86 release
1000 no conversion: 0 usecs
1000 with conversion: 0 usecs
1000000 no conversion: 1280 usecs
1000000 with conversion: 532 usecs
10000000 no conversion: 10403 usecs
10000000 with conversion: 5752 usecs
ldc x64 release
1000 no conversion: 0 usecs
1000 with conversion: 1 usecs
1000000 no conversion: 887 usecs
1000000 with conversion: 550 usecs
10000000 no conversion: 10730 usecs
10000000 with conversion: 5482 usecs
The results are strange, sometimes the conversion wins.
