FP magic with 32-bit

main.d

import std.stdio;

alias S = float;
float shL = 0x1.1b95eep-4; // -0.069235
float shR = 0x1.9c7cfep-7; // -0.012588

F fun(F)(F x)
{
    return 1.0 + x * 2;
}

S f1()
{
    S r = fun(shR);
    S l = fun(shL);
    return (r - l);
}

S f2()
{
    return (fun(shR) - fun(shL));
}

unittest
{
    writefln("f1: %a", f1());
    writefln("f2: %a", f2());
    assert(f1 == f2); // fails on 32-bit
}

output

f1: -0x1.d00cap-4
f2: -0x1.d00c9cp-4
core.exception.AssertError@en.d(28): unittest failure