ISPC Online Compiler
ISPC stands for Intel SPMD Program Compiler. It takes C-like code and compiles it to use SIMD instructions (SSE, AVX, AVX-512) on your CPU. The idea: you write code that looks like it operates on a single value, and ISPC automatically runs it across multiple data lanes in parallel. No intrinsics, no manual vectorization.
This matters for performance-critical code -- image processing, physics simulations, ray tracing, scientific computing. Hand-writing SIMD intrinsics is tedious and error-prone. ISPC gives you most of the performance with much less pain.
Why use an ISPC online compiler?
ISPC requires the Intel compiler toolchain and understanding of how it interfaces with C/C++ code through export functions. For learning the SPMD model or testing how ISPC handles a particular computation, an online compiler removes the build system complexity.
A simple ISPC export function
export void compute_mandelbrot(
uniform float x0[], uniform float y0[],
uniform int output[], uniform int count,
uniform int max_iter)
{
foreach (i = 0 ... count) {
float cx = x0[i];
float cy = y0[i];
float zx = 0.0f;
float zy = 0.0f;
int iter = 0;
while (iter < max_iter && (zx*zx + zy*zy) < 4.0f) {
float temp = zx*zx - zy*zy + cx;
zy = 2.0f * zx * zy + cy;
zx = temp;
iter++;
}
output[i] = iter;
}
}
The foreach construct is where the magic happens. Each iteration runs in a separate SIMD lane, so on an AVX2 machine, 8 iterations execute simultaneously. Variables without the uniform qualifier are "varying" -- each program instance (SIMD lane) has its own copy. uniform values are shared across all lanes. This distinction is what makes ISPC's performance model explicit without requiring you to think in terms of vector registers.
ISPC on OneCompiler
OneCompiler provides an ISPC environment where you can write and test ISPC functions. It's useful for understanding the SPMD programming model, experimenting with foreach and uniform/varying semantics, and seeing how the language handles control flow divergence across SIMD lanes.