[2/n]decouple quantization implementation from vLLM dependency (#8112)

Co-authored-by: walker-ai <yiyun.wyt@antgroup.com>
Co-authored-by: leoneo <1320612015@qq.com>

sgl-kernel/csrc/gemm/gptq/compat.cuh

@@ -0,0 +1,62 @@
+/*
+Copied from https://github.com/turboderp/exllamav2
+*/
+
+#ifndef _compat_cuh
+#define _compat_cuh
+
+namespace sglang {
+namespace gptq {
+// atomicAdd for half types, to support CC < 7.x
+
+__device__ __forceinline__ void atomicAdd_half(half* address, half val) {
+  unsigned int* address_as_ui = (unsigned int*)((char*)address - ((size_t)address & 2));
+  unsigned int old = *address_as_ui;
+  unsigned int assumed;
+
+  do {
+    assumed = old;
+    __half_raw hsum;
+    hsum.x = (size_t)address & 2 ? (old >> 16) : (old & 0xffff);
+    half tmpres = __hadd(hsum, val);
+    hsum = __half_raw(tmpres);
+    old = (size_t)address & 2 ? (old & 0xffff) | (hsum.x << 16) : (old & 0xffff0000) | hsum.x;
+    old = atomicCAS(address_as_ui, assumed, old);
+  } while (assumed != old);
+}
+
+// atomicAdd for half2 types
+
+__device__ __forceinline__ void atomicAdd_half2(half2* address, half2 val) {
+  unsigned int* address_as_ui = (unsigned int*)address;
+  unsigned int old = *address_as_ui;
+  unsigned int assumed;
+  do {
+    assumed = old;
+    half2 old_val = *((half2*)&old);
+    half2 new_val = __hadd2(old_val, val);
+    old = atomicCAS(address_as_ui, assumed, *((unsigned int*)&new_val));
+  } while (assumed != old);
+}
+
+//
+
+#if defined(__CUDA_ARCH__) || defined(USE_ROCM)
+#if __CUDA_ARCH__ < 700 || defined(USE_ROCM)
+
+__device__ __forceinline__ void atomicAdd(half* address, half val) {
+  atomicAdd_half(address, val);
+}
+
+#if __CUDA_ARCH__ < 600 || defined(USE_ROCM)
+__device__ __forceinline__ void atomicAdd(half2* address, half2 val) {
+  atomicAdd_half2(address, val);
+}
+#endif
+
+#endif
+#endif
+
+}  // namespace gptq
+}  // namespace sglang
+#endif