On Thu, 07 Jul 2011 14:19:05 -0400, Loopback <elliott.darf...@gmail.com>
wrote:
Hello!
I've been programming some miscellaneous code and got stuck in an odd
case. While comparing floats, two obviously identical values return
false in comparison.
I am not sure if this is related to float precision or something
similar. This is the code that I have used:
import std.stdio;
void main(string[] args)
{
while(foo()) {}
}
bool foo()
{
static bool ss;
static int loops;
static float m = 0f;
if(m != 1.73205f)
{
m += 0.00500592f;
if(++loops == 346)
ss = true;
}
if(ss)
{
writefln("Variable: %s", m);
writefln("Constant: %s", 1.73205f);
writefln("Equality: %s", m == 1.73205f);
return false;
}
return true;
}
The output of this program is the following:
Variable: 1.73205
Constant: 1.73205
Equality: false
My question is; how come these values compare unequal?
Because they aren't. Just because they are equal to 5 decimal places
(which by the way is an inaccurate printout of their value), does not mean
they are fully equal.
Be very careful when comparing floating point numbers. Generally you want
to use an epsilon to say they are "close enough".
-Steve
