Add GPTQ support (#916)

csrc/quantization/gptq/qdq_util.cuh

@@ -0,0 +1,60 @@
+/*
+Copied from https://github.com/turboderp/exllamav2
+*/
+
+#ifndef _qdq_util_cuh
+#define _qdq_util_cuh
+
+namespace vllm {
+namespace gptq {
+
+union half2_uint32
+{
+    uint32_t as_uint32;
+    half2 as_half2;
+    __device__ half2_uint32(uint32_t val) : as_uint32(val) {}
+    __device__ half2_uint32(half2 val) : as_half2(val) {}
+};
+
+union half_uint16
+{
+    uint16_t as_uint16;
+    half as_half;
+    __device__ half_uint16(uint16_t val) : as_uint16(val) {}
+    __device__ half_uint16(half val) : as_half(val) {}
+};
+
+// Max_scale premultiplied by 1/256
+
+__forceinline__ __device__ half dq_scale(const int qs, const half max_scale)
+{
+    int qs_i = qs + 1;
+    half qs_h = __int2half_rn(qs_i * qs_i);
+    qs_h = __hmul(qs_h, max_scale);
+    return qs_h;
+}
+
+__forceinline__ __device__ half dq(const int q, const int qzero, const half scale)
+{
+    return __hmul(__int2half_rn(q - qzero), scale);
+}
+
+__forceinline__ __device__ half dq_ns(const int q, const int qzero)
+{
+    //return __hsub(__int2half_rn(q), __int2half_rn(qzero));
+    return __int2half_rn(q - qzero);
+}
+
+__forceinline__ __device__ int exb(const uint32_t q, const int shift, const int mask)
+{
+    return (int)((q >> shift) & mask);
+}
+
+__forceinline__ __device__ int exb(const uint32_t q1, const uint32_t q0, const int shift, const int mask)
+{
+    return (int)(__funnelshift_rc(q0, q1, shift) & mask);
+}
+
+}  // namespace gptq
+}  // namespace vllm
+#endif