llama.cpp/ggml/src/ggml-vulkan/vulkan-shaders/dequant_iq4_xs.comp


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#version 450

#include "dequant_head.glsl"

layout(local_size_x = 256, local_size_y = 1, local_size_z = 1) in;

layout (binding = 0) readonly buffer A {block_iq4_xs data_a[];};
layout (binding = 1) writeonly buffer D {D_TYPE data_b[];};

void main() {
    // Each thread handles 1 subblock (1 scale and 32 quantized values)
    const uint ib = gl_WorkGroupID.x * 32 + gl_LocalInvocationID.x / 8;

    init_iq_shmem(gl_WorkGroupSize);

    if (ib >= p.nel / 256) {
        return;
    }

    const uint ib32 = gl_LocalInvocationID.x % 8;

    const float d = float(data_a[ib].d);
    // Scales are 6 bits
    const uint scale = ((data_a[ib].scales_l[ib32/2] >> (4 * (ib32 & 1))) & 0xF)
                     | (((data_a[ib].scales_h >> (2 * ib32)) & 3) << 4);
    const float dl = d * (int(scale) - 32);

    const uint b_idx = 256 * ib + 32 * ib32;
    const uint q_idx = 16 * ib32;
    [[unroll]] for (uint l = 0; l < 16; ++l) {
        data_b[b_idx + l +  0] = D_TYPE(dl * kvalues_iq4nl[data_a[ib].qs[q_idx + l] & 0xF]);
        data_b[b_idx + l + 16] = D_TYPE(dl * kvalues_iq4nl[data_a[ib].qs[q_idx + l] >>  4]);
    }
}