Benchmarking sigmoid function between C and D

[Arun Chandrasekaran]

On Saturday, 7 April 2018 at 19:14:27 UTC, Daniel Kozak wrote:
> or for ldc 
> http://docs.algorithm.dlang.io/latest/mir_math_common.html
>
> On Sat, Apr 7, 2018 at 9:10 PM, Daniel Kozak 
> <kozzi11 at gmail.com> wrote:
>
>> can you try it with c math functions?
>>
>> instead of std.math, try to use core.stdc.math
>>
>> On Sat, Apr 7, 2018 at 8:53 PM, Arun Chandrasekaran via 
>> Digitalmars-d-learn <digitalmars-d-learn at puremagic.com> wrote:
>>
>>> [...]

Much better with mir.math.common, still a bit slower than C (even 
with larger loops):

10^7 iterations using sigmoid1: 168 ms
10^7 iterations using sigmoid2: 39 ms

Also LDC optimized away the computation. So I had to modify the 
code a bit.

```
private auto sigmoid1_perf() {
     auto sw = StopWatch(AutoStart.yes);
     int i;
     float x, y = 0.0f;

     for (i = 0; i < 10; i++) {
         for (x = -5.0f; x <= 5.0f; x+=0.00001f) {
             y += sigmoid1(x);
         }
     }
     auto t = sw.peek.total!"msecs";
     return tuple(y, t);
}

private auto sigmoid2_perf() {
     auto sw = StopWatch(AutoStart.yes);
     int i;
     float x, y = 0.0f;
     for (i = 0; i < 10; i++) {
         for (x = -5.0f; x <= 5.0f; x+=0.00001f) {
             y += sigmoid2(x);
         }
     }
     auto t = sw.peek.total!"msecs";
     return tuple(y, t);
}
```