[GD-General] FLT_MIN

[Pierre T. <p.t...@wa...>]

Here's something I don't get....

I was looking for the smallest floating-point value F such as F^2 doesn't
underflow. So, I wrote something like :

F^2 = FLT_MIN ;
=> F = sqrtf ( FLT_MIN ) ;

Then, as a test, I wrote :

 const float HalfSqrtFMin = sqrtf(FLT_MIN) * 0.5f;
 const float f = HalfSqrtFMin*HalfSqrtFMin;

I was expecting f to be zero due to underflow. Yet it wasn't. That was my
first clue something weird was going on.

So I investigated a bit more and found that the floating-point value I was
looking for was 1.40130e-045, which gives zero once squared. This is the
floating-point value whose binary representation is 0x00000001.

I've always thought FLT_MIN was the "min positive value" (as stated in
Float.h). What the hell is that number then ? I'm sure I'm missing something
obvious....

Pierre

PS:  http://www.codercorner.com/FPU.jpg