On 01/24/2012 04:13 AM, Caligo wrote:
alias double Real;
//alias float Real;
// simple linear interpolation; I partitioned the internals to help me
figure out what was happening.
Real lerp(Real t, Real a, Real b){
Real s1 = (1.0 - t) * a;
Real s2 = t * b;
Real rt1 = s1 + s2;
Real rt2 = ((1.0 - t) * a) + (t * b);
writefln("t=%.2f, a=%.2f, b=%.2f, s1=%.2f, s2=%.2f, rt1=%.2f,
rt2=%.2f :::", t, a, b, s1, s2, rt1, rt2);
return rt2;
}
unittest{
writeln(lerp(0.75, -2.0, 2.0)); // the correct result is 1.0
}
compile and run with 'dmd -inline -unittest' and the output should be:
t=0.75, a=-2.00, b=2.00, s1=-0.50, s2=1.50, rt1=1.00, rt2=1.00 :::
1
Now, change 'Real' to float by uncommenting the second line and
compile and run with 'dmd -unittest'. This is what I get for the
output:
t=0.75, a=0.00, b=2.00, s1=-0.50, s2=0.00, rt1=-0.50, rt2=1.50 :::
1.5
This: (with float)
writefln("t=%.2f, a=%.2f, b=%.2f, s1=%.2f, s2=%.2f, rt1=%.2f,
rt2=%.2f :::", t, a, b, s1, s2, rt1, rt2);
writefln("t=%.2f, a=%f, b=%.2f, s1=%.2f, s2=%.2f, rt1=%.2f, rt2=%.2f
:::", t, a, b, s1, s2, rt1, rt2);
Outputs: (with float)
t=0.75, a=0.00, b=2.00, s1=-0.50, s2=0.00, rt1=-0.50, rt2=1.50 :::
t=0.75, a=-2.000000, b=2.00, s1=-0.50, s2=0.00, rt1=-0.50, rt2=1.50 :::
difference:
%.2f ---> %f
I have no idea why 'a' is zero. 'rt1' and 'rt2' do not have the same
value, and 'lerp' does not return 1.0. Compiling with 'dmd -inline
-unittest' does produce the correct result as before, though.
You can play with different compiler options, such as -O, to get the
same weird behavior.
I presume this is another DMD bug?
