102 lines
4.1 KiB
Plaintext
102 lines
4.1 KiB
Plaintext
/*
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Adapted from https://github.com/mit-han-lab/llm-awq
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Modified from NVIDIA FasterTransformer:
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https://github.com/NVIDIA/FasterTransformer/blob/main/src/fastertransformer/cutlass_extensions/include/cutlass_extensions/interleaved_numeric_conversion.h
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@article{lin2023awq,
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title={AWQ: Activation-aware Weight Quantization for LLM Compression and
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Acceleration}, author={Lin, Ji and Tang, Jiaming and Tang, Haotian and Yang,
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Shang and Dang, Xingyu and Han, Song}, journal={arXiv}, year={2023}
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}
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*/
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#pragma once
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namespace vllm {
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namespace awq {
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__device__ uint4 dequantize_s4_to_fp16x2(uint32_t const& source) {
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#if defined(__CUDA_ARCH__) && __CUDA_ARCH__ < 750
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assert(false);
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#else
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uint4 result;
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uint32_t* h = reinterpret_cast<uint32_t*>(&result);
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uint32_t const i4s = reinterpret_cast<uint32_t const&>(source);
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// First, we extract the i4s and construct an intermediate fp16 number.
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static constexpr uint32_t immLut = (0xf0 & 0xcc) | 0xaa;
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static constexpr uint32_t BOTTOM_MASK = 0x000f000f;
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static constexpr uint32_t TOP_MASK = 0x00f000f0;
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static constexpr uint32_t I4s_TO_F16s_MAGIC_NUM = 0x64006400;
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// Note that the entire sequence only requires 1 shift instruction. This is
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// thanks to the register packing format and the fact that we force our
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// integers to be unsigned, and account for this in the fp16 subtractions. In
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// addition, I exploit the fact that sub and fma have the same throughput in
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// order to convert elt_23 and elt_67 to fp16 without having to shift them to
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// the bottom bits before hand.
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// Shift right by 8 to now consider elt_45 and elt_67. Issue first to hide RAW
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// dependency if we issue immediately before required.
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const uint32_t top_i4s = i4s >> 8;
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// Extract elt_01 - (i4s & 0x000f000f) | 0x64006400
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asm volatile("lop3.b32 %0, %1, %2, %3, %4;\n"
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: "=r"(h[0])
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: "r"(i4s), "n"(BOTTOM_MASK), "n"(I4s_TO_F16s_MAGIC_NUM),
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"n"(immLut));
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// Extract elt_23 (i4s & 0x00f000f0) | 0x64006400
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asm volatile("lop3.b32 %0, %1, %2, %3, %4;\n"
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: "=r"(h[1])
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: "r"(i4s), "n"(TOP_MASK), "n"(I4s_TO_F16s_MAGIC_NUM),
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"n"(immLut));
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// Extract elt_45 (top_i4s & 0x000f000f) | 0x64006400
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asm volatile("lop3.b32 %0, %1, %2, %3, %4;\n"
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: "=r"(h[2])
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: "r"(top_i4s), "n"(BOTTOM_MASK), "n"(I4s_TO_F16s_MAGIC_NUM),
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"n"(immLut));
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// Extract elt_67 (top_i4s & 0x00f000f0) | 0x64006400
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asm volatile("lop3.b32 %0, %1, %2, %3, %4;\n"
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: "=r"(h[3])
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: "r"(top_i4s), "n"(TOP_MASK), "n"(I4s_TO_F16s_MAGIC_NUM),
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"n"(immLut));
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// I use inline PTX below because I am not sure if the compiler will emit
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// float2half instructions if I use the half2 ctor. In this case, I chose
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// performance reliability over code readability.
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// This is the half2 {1032, 1032} represented as an integer.
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// static constexpr uint32_t FP16_TOP_MAGIC_NUM = 0x64086408;
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// Haotian: subtract {1024, 1024} instead, we do not need to map to [-8, 7]
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static constexpr uint32_t FP16_TOP_MAGIC_NUM = 0x64006400;
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// This is the half2 {1 / 16, 1 / 16} represented as an integer.
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static constexpr uint32_t ONE_SIXTEENTH = 0x2c002c00;
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// This is the half2 {-72, -72} represented as an integer.
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// static constexpr uint32_t NEG_72 = 0xd480d480;
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// Haotian: Let's use {-64, -64}.
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static constexpr uint32_t NEG_64 = 0xd400d400;
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// Finally, we construct the output numbers.
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// Convert elt_01
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asm volatile("sub.f16x2 %0, %1, %2;\n"
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: "=r"(h[0])
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: "r"(h[0]), "r"(FP16_TOP_MAGIC_NUM));
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// Convert elt_23
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asm volatile("fma.rn.f16x2 %0, %1, %2, %3;\n"
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: "=r"(h[1])
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: "r"(h[1]), "r"(ONE_SIXTEENTH), "r"(NEG_64));
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// Convert elt_45
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asm volatile("sub.f16x2 %0, %1, %2;\n"
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: "=r"(h[2])
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: "r"(h[2]), "r"(FP16_TOP_MAGIC_NUM));
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// Convert elt_67
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asm volatile("fma.rn.f16x2 %0, %1, %2, %3;\n"
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: "=r"(h[3])
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: "r"(h[3]), "r"(ONE_SIXTEENTH), "r"(NEG_64));
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return result;
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#endif
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}
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} // namespace awq
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} // namespace vllm
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