Question

I am working in C to implement pseudo-code that says:

delay = ROUND(64*(floatDelay - intDelay)) where intDelay = (int) floatDelay 

The floatDelay will always be positive. Is there an advantage to using the round function from math.h:

#inlcude <math.h> delay=(int) round(64*(floatDelay-intDelay)); 

or can I use:

delay=(int)(64*(floatDelay - intDelay) + 0.5)) 

Answer 1

You should always use the appropriate math libs when dealing with floating point numbers. A float may be only a very close approximation of the actual value, and that can cause weirdness.

For instance, 5f might be approximated to 4.9999999… and if you try to cast directly to int it will be truncated to 4.

To see why in depth, you should look up floating point numbers on wikipedia. But in short instead of storing the number as a straight series of bits like an int, it’s stored in two parts. There’s a ‘fraction’ and an exponent, where the final value of the float is fraction * (base ^ exponent).