FP precision with sin

main.d

void main() {
    import std.stdio;
    import std.meta : AliasSeq;
    import std.math : PI, sin;
    import core.stdc.math : sin_c = sin;
    foreach (S; AliasSeq!(float, double, real))
    {
        S pi = PI;
        writefln("x: %12s, x_c: %12s, x_c_pi: %12s", sin(S(PI)), sin_c(S(PI)), sin_c(pi));
    }
}

output

> rdmd main.d

x: -8.74228e-08, x_c:  1.22465e-16, x_c_pi: -8.74228e-08
x:  1.22461e-16, x_c:  1.22465e-16, x_c_pi:  1.22465e-16
x: -5.42101e-20, x_c:  1.22465e-16, x_c_pi:  1.22465e-16