Clarification question on "void planVulkanFFTAxis(VulkanFFTPlan* vulkanFFTPlan, uint32_t axis)"

[shuwang1]

Hi Lichtso,

May I ask what the codes below are for?

void planVulkanFFTAxis(VulkanFFTPlan* vulkanFFTPlan, uint32_t axis) {
    VulkanFFTAxis* vulkanFFTAxis = &vulkanFFTPlan->axes[axis];

    {
        vulkanFFTAxis->stageCount = 31-__builtin_clz(vulkanFFTAxis->sampleCount); // Logarithm of base 2
        vulkanFFTAxis->stageRadix = (uint32_t*)malloc(sizeof(uint32_t) * vulkanFFTAxis->stageCount);
        uint32_t stageSize = vulkanFFTAxis->sampleCount;
        vulkanFFTAxis->stageCount = 0;
        while(stageSize > 1) {
            uint32_t radixIndex = SUPPORTED_RADIX_LEVELS;
            do {
                assert(radixIndex > 0);
                --radixIndex;
                vulkanFFTAxis->stageRadix[vulkanFFTAxis->stageCount] = 2<<radixIndex;
            } while(stageSize % vulkanFFTAxis->stageRadix[vulkanFFTAxis->stageCount] > 0);
            stageSize /= vulkanFFTAxis->stageRadix[vulkanFFTAxis->stageCount];
            ++vulkanFFTAxis->stageCount;
        }
    }

Thank you!

[Lichtso]

It takes uint32_t axis and vulkanFFTPlan->axes[axis].sampleCount as input and then calculates stageCount and stageRadix[] from that.

The "stages" refer to the iterations in this algorithm: https://en.wikipedia.org/wiki/Cooley%E2%80%93Tukey_FFT_algorithm