Performance of integer and bitwise operations on GPU

Question

Though GPUs are supposed for use with floating point data types, I'd be interested in how fast can GPU process bitwise operations. These are the fastest possible on CPU, but does GPU emulate bitwise operations or are they fully computed on hardware? I'm planning to use them inside shader programs written with GLSL. Also I'd suppose that if bitwise operations have full preformance, integer data types should have also, but I need confirmation on that.

To be more precise, targeted versions are OpenGL 3.2 and GLSL 1.5. Hardware that should run this is any Radeon HD graphics card and GeForce series 8 and newer.. If there are some major changes in newer versions of OpenGL and GLSL related to processing speeds of bitwise operations/integers, I'd be glad if you'll point them out.

You need to specify a particular GPU architecture, or at least OpenGL version. Right now this question is horribly vague. — Ben Voigt
@BenVoigt updated, is it precise enough, or you need specific code name of architecture (they change them like for every new card) — Raven
Raven: There are some huge changes between Radeon HD 1xxx and HD 7xxx, but that extra information is a big improvement. Assuming that you're looking at cards which advertise OpenGL 3.2 support (or later), that's probably clear enough. — Ben Voigt

Louis Ricci Louis Ricci · Accepted Answer · 2012-01-03T16:05:29

This question was partially answered Integer calculations on GPU

In short modern GPUs have equivalent INT and FP performance for 32bit data. So your logical operations will run at the same speed.

From a programming perspective you will lose performance if you are dealing with SCALAR integer data. GPUs like working with PARALLEL and PACKED operations.

for(int i=0; i<LEN_VEC4; i++)
    VEC4[i] = VEC4[i] * VEC4[i]; // (x,y,z,w) * (x,y,z,w)

If you're doing something like...

for(int i=0; i<LEN_VEC4; i++)
    VEC4[i].w = (VEC4[i].x & 0xF0F0F0F0) | (VEC4[i].z ^ 0x0F0F0F0F) ^ VEC4[i].w;

...doing many different operations on elements of the same vector you will run into performance problems.

Performance of integer and bitwise operations on GPU

1 Answers