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ck_tile: add FillUniformScaleDistribution and fix MX GEMM scale init (#7724) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ## Summary ### Problem MX GEMM pipeline tests were passing vacuously: scale bytes were drawn from a fixed range (40–60) which, for e8m0, maps to scales ≈ 10⁻²⁷ — far below FP16 min denorm. Both GPU and CPU produced all-zero outputs, so numerical checks passed without exercising the GEMM. ### Changes **`include/ck_tile/host/fill.hpp`** — new `FillUniformScaleDistribution<ScaleType>` functor - Accepts human-readable float bounds and maps them to the raw byte range of any ExMy scale type (e8m0, e4m3, e5m3) by re-centering the IEEE 754 exponent into the type's bias space - Sampling is uniform over raw bytes → uniform over representable values - Fixes left-shift UB: uses multiplication instead of `<< mant_bits` to avoid shifting negative signed integers (C++17 UB) - Adds `assert(min_r <= max_r)` to catch inverted-range UB when both bounds exceed the type's representable range - Provides default member values (0.125f, 2.0f) and `std::optional` seed consistent with sibling fillers - `/** */` Doxygen style with `@note` on snapping asymmetry **`test/ck_tile/gemm_mx/test_mx_gemm_pipeline_util.hpp`** — fix scale initialization - Replace manual byte-range distribution with `FillUniformScaleDistribution<>{0.125f, 2.0f}` - Use distinct seeds for scale_a (11941) and scale_b (11943) to avoid correlated scale tensors that were causing 60 test failures for fp4+e5m3/e4m3 combinations **`test/ck_tile/utility/test_fill.cpp`** — new unit tests for `FillUniformScaleDistribution` - 16 typed tests across e8m0, e4m3, e5m3: validity, range, reproducibility, coverage, snapping, stress, nullopt seed, and range overload - Test helper `expected_raw_range` mirrors implementation clamping exactly