Float modulo operator that includes the upper value

Question

I need an efficient glsl code that doesn't have if-else statement. Currently the algorithm is like this :

lowp float a;
if (a > 1.0) 
   a -= 1.0;
else if (a < 0.0) 
   a += 1.0;

It's similar with a floating point modulo operator :

a = mod(a,1.0);

only if a == 1, it should return 1, instead of 0.

How to do this without if-else though?

Thanks

Answer 1

Here is a mathematic representation that might do what you need - without using branching statements

For inputs between [-1, 2.0]

a = a + 1 - max(trunc(a), ceil(a))

Input   Output
0.3     0.3
-0.3    0.7
0.7     0.7
1.3     0.3
1.7     0.7
1       1.0