import torch
import torch.nn as nn
from torch.utils.cpp_extension import load_inline

class ModelNew(nn.Module):
    def __init__(self, a=1.0):
        super().__init__()
        self.a = a
        self._compile_cuda_kernel()

    def _compile_cuda_kernel(self):
        cpp_source = """
        torch::Tensor isru_cuda(torch::Tensor x, float a);
        """

        cuda_source = """
        #include <torch/extension.h>
        #include <cuda_runtime.h>
        #include <math.h>

        __device__ __forceinline__ float isru_op(float x, float a) {
            // f(x) = x / sqrt(1 + a * x^2)
            float denom = sqrtf(1.0f + a * x * x);
            return x / denom;
        }

        __global__ void isru_kernel(
            const float* __restrict__ x,
            float* __restrict__ output,
            const int n_elements,
            const float a) 
        {
            const int tid = blockIdx.x * blockDim.x + threadIdx.x;
            const int stride = blockDim.x * gridDim.x;

            const int vec_loops = n_elements >> 2;
            const float4* x_vec = reinterpret_cast<const float4*>(x);
            float4* out_vec = reinterpret_cast<float4*>(output);

            for (int i = tid; i < vec_loops; i += stride) {
                float4 v = __ldg(&x_vec[i]);
                float4 r;

                r.x = isru_op(v.x, a);
                r.y = isru_op(v.y, a);
                r.z = isru_op(v.z, a);
                r.w = isru_op(v.w, a);

                out_vec[i] = r;
            }

            const int tail_start = vec_loops << 2;
            for (int i = tail_start + tid; i < n_elements; i += stride) {
                output[i] = isru_op(x[i], a);
            }
        }

        torch::Tensor isru_cuda(torch::Tensor x, float a) {
            auto x_c = x.contiguous();
            const int n_elements = x_c.numel();
            auto output = torch::empty_like(x_c);

            const int threads = 256;
            const int max_blocks = 65535;
            const int blocks = std::min((n_elements + threads * 4 - 1) / (threads * 4), max_blocks);

            isru_kernel<<<blocks, threads>>>(
                x_c.data_ptr<float>(),
                output.data_ptr<float>(),
                n_elements,
                a
            );

            return output;
        }
        """

        self.op = load_inline(
            name="isru_v1",
            cpp_sources=cpp_source,
            cuda_sources=cuda_source,
            functions=["isru_cuda"],
            extra_cuda_cflags=["-O3", "--use_fast_math"],
            verbose=False
        )

    def forward(self, x):
        return self.op.isru_cuda(x, self.a)