"""Persistent SM120 CUDA decode with fused norms and split-KV attention."""

from __future__ import annotations

import os
import sys

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


HIDDEN = 1024
INTERMEDIATE = 3072
NUM_Q = 16
NUM_KV = 8
HEAD_DIM = 128
NUM_LAYERS = 4
EPS = 1e-6


class Block(nn.Module):
    def __init__(self):
        super().__init__()
        self.input_ln = nn.Parameter(torch.ones(1024, dtype=torch.bfloat16))
        self.q_proj = nn.Parameter(torch.empty(2048, 1024, dtype=torch.bfloat16))
        self.k_proj = nn.Parameter(torch.empty(1024, 1024, dtype=torch.bfloat16))
        self.v_proj = nn.Parameter(torch.empty(1024, 1024, dtype=torch.bfloat16))
        self.q_norm = nn.Parameter(torch.ones(128, dtype=torch.bfloat16))
        self.k_norm = nn.Parameter(torch.ones(128, dtype=torch.bfloat16))
        self.o_proj = nn.Parameter(torch.empty(1024, 2048, dtype=torch.bfloat16))
        self.post_ln = nn.Parameter(torch.ones(1024, dtype=torch.bfloat16))
        self.gate_proj = nn.Parameter(torch.empty(3072, 1024, dtype=torch.bfloat16))
        self.up_proj = nn.Parameter(torch.empty(3072, 1024, dtype=torch.bfloat16))
        self.down_proj = nn.Parameter(torch.empty(1024, 3072, dtype=torch.bfloat16))
        for parameter in self.parameters():
            if parameter.ndim == 2:
                nn.init.normal_(parameter, std=0.02)


class Model(nn.Module):
    def __init__(self, num_layers: int = NUM_LAYERS, max_seq: int = 131072):
        super().__init__()
        self.num_layers = num_layers
        self.max_seq = max_seq
        self.blocks = nn.ModuleList([Block() for _ in range(num_layers)])
        self._engine = None


_CPP = r"""
#include <torch/extension.h>
void launch_decode(torch::Tensor weights, torch::Tensor caches,
                   torch::Tensor hidden, torch::Tensor noise,
                   torch::Tensor rope, torch::Tensor workspace,
                   int64_t start, int64_t steps, int64_t layers,
                   int64_t capacity, int64_t blocks);
int64_t resident_blocks();
"""

_CUDA = r"""
#include <torch/extension.h>
#include <ATen/cuda/CUDAContext.h>
#include <c10/cuda/CUDAException.h>
#include <cuda_bf16.h>
#include <math_constants.h>
#include <cooperative_groups.h>

namespace cg = cooperative_groups;
using bf16 = __nv_bfloat16;

struct Layer {
    const bf16* input_ln;
    const bf16* q_proj;
    const bf16* k_proj;
    const bf16* v_proj;
    const bf16* q_norm;
    const bf16* k_norm;
    const bf16* o_proj;
    const bf16* post_ln;
    const bf16* gate_proj;
    const bf16* up_proj;
    const bf16* down_proj;
};

__device__ __forceinline__ float warp_sum(float value) {
    #pragma unroll
    for (int offset = 16; offset; offset >>= 1)
        value += __shfl_xor_sync(0xffffffff, value, offset);
    return value;
}

__device__ __forceinline__ float4 unpack(uint2 bits) {
    bf16* values = reinterpret_cast<bf16*>(&bits);
    return make_float4(__bfloat162float(values[0]), __bfloat162float(values[1]),
                       __bfloat162float(values[2]), __bfloat162float(values[3]));
}

__device__ __forceinline__ float4 weight4(const bf16* address) {
    return unpack(__ldg(reinterpret_cast<const uint2*>(address)));
}

__device__ __forceinline__ uint2 stream2(const bf16* address) {
    uint2 bits;
    asm volatile("ld.global.cs.v2.u32 {%0, %1}, [%2];"
                 : "=r"(bits.x), "=r"(bits.y) : "l"(address));
    return bits;
}

__device__ __forceinline__ float dot4(float4 left, float4 right, float sum) {
    sum = fmaf(left.x, right.x, sum);
    sum = fmaf(left.y, right.y, sum);
    sum = fmaf(left.z, right.z, sum);
    return fmaf(left.w, right.w, sum);
}

__device__ __forceinline__ float mix_value(const bf16* hidden, const bf16* noise,
                                          int index, bool mix) {
    float value = __bfloat162float(hidden[index]);
    if (mix) {
        float left = __bfloat162float(__float2bfloat16_rn(0.5f * value));
        float right = __bfloat162float(__float2bfloat16_rn(
            0.5f * __bfloat162float(noise[index])));
        value = __bfloat162float(__float2bfloat16_rn(left + right));
    }
    return value;
}

__device__ __forceinline__ void normalized_input(
    float4 (&activation)[8], const bf16* hidden, const bf16* noise,
    const bf16* norm, bool mix) {
    int lane = threadIdx.x & 31;
    float square_sum = 0.0f;
    #pragma unroll
    for (int chunk = 0; chunk < 8; ++chunk) {
        int column = chunk * 128 + lane * 4;
        float4 values = make_float4(
            mix_value(hidden, noise, column, mix),
            mix_value(hidden, noise, column + 1, mix),
            mix_value(hidden, noise, column + 2, mix),
            mix_value(hidden, noise, column + 3, mix));
        activation[chunk] = values;
        square_sum = dot4(values, values, square_sum);
    }
    float scale = rsqrtf(warp_sum(square_sum) * (1.0f / 1024.0f) + 1e-6f);
    #pragma unroll
    for (int chunk = 0; chunk < 8; ++chunk) {
        float4 norm_values = weight4(norm + chunk * 128 + lane * 4);
        activation[chunk].x = (activation[chunk].x * scale) * norm_values.x;
        activation[chunk].y = (activation[chunk].y * scale) * norm_values.y;
        activation[chunk].z = (activation[chunk].z * scale) * norm_values.z;
        activation[chunk].w = (activation[chunk].w * scale) * norm_values.w;
    }
}

__device__ __forceinline__ void normalized_post(
    float4 (&activation)[8], const float* residual, const bf16* norm) {
    int lane = threadIdx.x & 31;
    float square_sum = 0.0f;
    #pragma unroll
    for (int chunk = 0; chunk < 8; ++chunk) {
        float4 values = reinterpret_cast<const float4*>(residual)[chunk * 32 + lane];
        activation[chunk] = values;
        square_sum = dot4(values, values, square_sum);
    }
    float scale = rsqrtf(warp_sum(square_sum) * (1.0f / 1024.0f) + 1e-6f);
    #pragma unroll
    for (int chunk = 0; chunk < 8; ++chunk) {
        float4 norm_values = weight4(norm + chunk * 128 + lane * 4);
        activation[chunk].x = (activation[chunk].x * scale) * norm_values.x;
        activation[chunk].y = (activation[chunk].y * scale) * norm_values.y;
        activation[chunk].z = (activation[chunk].z * scale) * norm_values.z;
        activation[chunk].w = (activation[chunk].w * scale) * norm_values.w;
    }
}

__device__ __forceinline__ void store4(bf16* address, float4 value) {
    uint2 bits;
    auto pairs = reinterpret_cast<__nv_bfloat162*>(&bits);
    pairs[0] = __floats2bfloat162_rn(value.x, value.y);
    pairs[1] = __floats2bfloat162_rn(value.z, value.w);
    *reinterpret_cast<uint2*>(address) = bits;
}

__device__ __forceinline__ void normalize_rotate(
    float4 (&values)[4], const bf16* norm, const float* angles, int group_lane) {
    float variance = 0.0f;
    #pragma unroll
    for (int chunk = 0; chunk < 4; ++chunk)
        variance = dot4(values[chunk], values[chunk], variance);
    unsigned mask = 0xffu << (threadIdx.x & 24);
    #pragma unroll
    for (int offset = 4; offset; offset >>= 1)
        variance += __shfl_xor_sync(mask, variance, offset, 8);
    float scale = rsqrtf(variance * (1.0f / 128.0f) + 1e-6f);
    #pragma unroll
    for (int chunk = 0; chunk < 4; ++chunk) {
        float4 learned = weight4(norm + chunk * 32 + group_lane * 4);
        values[chunk].x = (values[chunk].x * scale) * learned.x;
        values[chunk].y = (values[chunk].y * scale) * learned.y;
        values[chunk].z = (values[chunk].z * scale) * learned.z;
        values[chunk].w = (values[chunk].w * scale) * learned.w;
    }
    #pragma unroll
    for (int chunk = 0; chunk < 2; ++chunk) {
        float4 cosine = reinterpret_cast<const float4*>(angles)[chunk * 8 + group_lane];
        float4 sine = reinterpret_cast<const float4*>(angles + 64)[chunk * 8 + group_lane];
        float4 first = values[chunk];
        float4 second = values[chunk + 2];
        values[chunk].x = __fsub_rn(__fmul_rn(first.x, cosine.x), __fmul_rn(second.x, sine.x));
        values[chunk].y = __fsub_rn(__fmul_rn(first.y, cosine.y), __fmul_rn(second.y, sine.y));
        values[chunk].z = __fsub_rn(__fmul_rn(first.z, cosine.z), __fmul_rn(second.z, sine.z));
        values[chunk].w = __fsub_rn(__fmul_rn(first.w, cosine.w), __fmul_rn(second.w, sine.w));
        values[chunk + 2].x = __fadd_rn(__fmul_rn(first.x, sine.x), __fmul_rn(second.x, cosine.x));
        values[chunk + 2].y = __fadd_rn(__fmul_rn(first.y, sine.y), __fmul_rn(second.y, cosine.y));
        values[chunk + 2].z = __fadd_rn(__fmul_rn(first.z, sine.z), __fmul_rn(second.z, cosine.z));
        values[chunk + 2].w = __fadd_rn(__fmul_rn(first.w, sine.w), __fmul_rn(second.w, cosine.w));
    }
}

__global__ __launch_bounds__(256, 2) void persistent_decode(
    const Layer* __restrict__ weights, bf16* const* __restrict__ caches,
    bf16* __restrict__ hidden, const bf16* __restrict__ noise,
    const float* __restrict__ rope, float* __restrict__ workspace,
    int start, int steps, int layers, int capacity) {
    cg::grid_group grid = cg::this_grid();
    int thread = threadIdx.x;
    int lane = thread & 31;
    int warp = thread >> 5;
    int block = blockIdx.x;
    int blocks = gridDim.x;
    int splits = blocks / 8;
    float* qkv = workspace;
    float* attention = qkv + 4096;
    float* residual = attention + 2048;
    float* intermediate = residual + 1024;
    float* partial = intermediate + 3072;
    __shared__ float shared[32 * 2 * 132];

    for (int step = 0; step < steps; ++step) {
        int position = start + step;
        const bf16* step_noise = noise + int64_t(step) * 1024;
        for (int layer_index = 0; layer_index < layers; ++layer_index) {
            const Layer& layer = weights[layer_index];
            bool mix = layer_index == 0;
            bf16* key_cache = caches[layer_index * 2];
            bf16* value_cache = caches[layer_index * 2 + 1];
            {
                float4 activation[8];
                normalized_input(activation, hidden, step_noise, layer.input_ln, mix);
                for (int row = block * 8 + warp; row < 4096; row += blocks * 8) {
                    const bf16* matrix = row < 2048 ? layer.q_proj :
                                         row < 3072 ? layer.k_proj : layer.v_proj;
                    int matrix_row = row < 2048 ? row : row & 1023;
                    const bf16* row_data = matrix + matrix_row * 1024;
                    float sum = 0.0f;
                    #pragma unroll
                    for (int chunk = 0; chunk < 8; ++chunk)
                        sum = dot4(weight4(row_data + chunk * 128 + lane * 4),
                                   activation[chunk], sum);
                    sum = warp_sum(sum);
                    if (lane == 0) qkv[row] = sum;
                }
            }
            grid.sync();

            {
                int kv_head = block % 8;
                int split = block / 8;
                int begin = (int64_t(position + 1) * split) / splits;
                int end = (int64_t(position + 1) * (split + 1)) / splits;
                int group = thread / 8;
                int group_lane = thread % 8;
                unsigned mask = 0xffu << (lane & 24);
                float4 query_first[4];
                float4 query_second[4];
                float4 accumulator_first[4];
                float4 accumulator_second[4];
                #pragma unroll
                for (int chunk = 0; chunk < 4; ++chunk) {
                    query_first[chunk] = reinterpret_cast<float4*>(qkv + kv_head * 256)[chunk * 8 + group_lane];
                    query_second[chunk] = reinterpret_cast<float4*>(qkv + kv_head * 256 + 128)[chunk * 8 + group_lane];
                    accumulator_first[chunk] = make_float4(0, 0, 0, 0);
                    accumulator_second[chunk] = make_float4(0, 0, 0, 0);
                }
                const float* angles = rope + int64_t(position) * 128;
                normalize_rotate(query_first, layer.q_norm, angles, group_lane);
                normalize_rotate(query_second, layer.q_norm, angles, group_lane);
                if (split == splits - 1 && group == 0) {
                    float4 key[4];
                    #pragma unroll
                    for (int chunk = 0; chunk < 4; ++chunk)
                        key[chunk] = reinterpret_cast<float4*>(qkv + 2048 + kv_head * 128)[chunk * 8 + group_lane];
                    normalize_rotate(key, layer.k_norm, angles, group_lane);
                    #pragma unroll
                    for (int chunk = 0; chunk < 4; ++chunk) {
                        int dimension = chunk * 32 + group_lane * 4;
                        int64_t offset = (int64_t(kv_head) * capacity + position) * 128 + dimension;
                        store4(key_cache + offset, key[chunk]);
                        store4(value_cache + offset,
                            reinterpret_cast<float4*>(qkv + 3072 + kv_head * 128)[chunk * 8 + group_lane]);
                    }
                }
                __syncthreads();
                float maximum_first = -CUDART_INF_F;
                float maximum_second = -CUDART_INF_F;
                float denominator_first = 0.0f;
                float denominator_second = 0.0f;
                for (int [REDACTED credential assignment] + group; token < end; token += 64) {
                    uint2 key_bits[2][4];
                    uint2 value_bits[2][4];
                    #pragma unroll
                    for (int item = 0; item < 2; ++item) {
                        #pragma unroll
                        for (int chunk = 0; chunk < 4; ++chunk) {
                            int64_t offset = (int64_t(kv_head) * capacity + token + item * 32) * 128 + chunk * 32 + group_lane * 4;
                            if (token + item * 32 < end) {
                                key_bits[item][chunk] = stream2(key_cache + offset);
                                value_bits[item][chunk] = stream2(value_cache + offset);
                            }
                        }
                    }
                    #pragma unroll
                    for (int item = 0; item < 2; ++item) {
                        if (token + item * 32 < end) {
                            float score_first = 0.0f;
                            float score_second = 0.0f;
                            #pragma unroll
                            for (int chunk = 0; chunk < 4; ++chunk) {
                                float4 key = unpack(key_bits[item][chunk]);
                                score_first = dot4(query_first[chunk], key, score_first);
                                score_second = dot4(query_second[chunk], key, score_second);
                            }
                            #pragma unroll
                            for (int offset = 4; offset; offset >>= 1) {
                                score_first += __shfl_xor_sync(mask, score_first, offset, 8);
                                score_second += __shfl_xor_sync(mask, score_second, offset, 8);
                            }
                            score_first *= 0.08838834764831845f;
                            score_second *= 0.08838834764831845f;
                            float next_first = fmaxf(maximum_first, score_first);
                            float next_second = fmaxf(maximum_second, score_second);
                            float correction_first = __expf(maximum_first - next_first);
                            float correction_second = __expf(maximum_second - next_second);
                            float probability_first = __expf(score_first - next_first);
                            float probability_second = __expf(score_second - next_second);
                            denominator_first = denominator_first * correction_first + probability_first;
                            denominator_second = denominator_second * correction_second + probability_second;
                            #pragma unroll
                            for (int chunk = 0; chunk < 4; ++chunk) {
                                float4 value = unpack(value_bits[item][chunk]);
                                accumulator_first[chunk].x = accumulator_first[chunk].x * correction_first + probability_first * value.x;
                                accumulator_first[chunk].y = accumulator_first[chunk].y * correction_first + probability_first * value.y;
                                accumulator_first[chunk].z = accumulator_first[chunk].z * correction_first + probability_first * value.z;
                                accumulator_first[chunk].w = accumulator_first[chunk].w * correction_first + probability_first * value.w;
                                accumulator_second[chunk].x = accumulator_second[chunk].x * correction_second + probability_second * value.x;
                                accumulator_second[chunk].y = accumulator_second[chunk].y * correction_second + probability_second * value.y;
                                accumulator_second[chunk].z = accumulator_second[chunk].z * correction_second + probability_second * value.z;
                                accumulator_second[chunk].w = accumulator_second[chunk].w * correction_second + probability_second * value.w;
                            }
                            maximum_first = next_first;
                            maximum_second = next_second;
                        }
                    }
                }
                float* first_state = shared + group * 264;
                float* second_state = first_state + 132;
                #pragma unroll
                for (int chunk = 0; chunk < 4; ++chunk) {
                    reinterpret_cast<float4*>(first_state)[chunk * 8 + group_lane] = accumulator_first[chunk];
                    reinterpret_cast<float4*>(second_state)[chunk * 8 + group_lane] = accumulator_second[chunk];
                }
                if (group_lane == 0) {
                    first_state[128] = maximum_first;
                    first_state[129] = denominator_first;
                    second_state[128] = maximum_second;
                    second_state[129] = denominator_second;
                }
                __syncthreads();
                int query_in_pair = thread / 128;
                int dimension = thread % 128;
                float maximum = -CUDART_INF_F;
                #pragma unroll
                for (int other_group = 0; other_group < 32; ++other_group)
                    maximum = fmaxf(maximum, shared[other_group * 264 + query_in_pair * 132 + 128]);
                float numerator = 0.0f;
                float denominator = 0.0f;
                #pragma unroll
                for (int other_group = 0; other_group < 32; ++other_group) {
                    const float* state = shared + other_group * 264 + query_in_pair * 132;
                    float correction = state[129] > 0 ? __expf(state[128] - maximum) : 0.0f;
                    numerator += state[dimension] * correction;
                    denominator += state[129] * correction;
                }
                float* destination = partial + block * 264 + query_in_pair * 132;
                destination[dimension] = numerator;
                if (dimension == 0) {
                    destination[128] = maximum;
                    destination[129] = denominator;
                }
            }
            grid.sync();

            if (block < 16) {
                int kv_head = block / 2;
                int query_in_pair = block % 2;
                const float* source = partial + kv_head * 264 + query_in_pair * 132;
                float maximum = thread < splits ? source[thread * 2112 + 128] : -CUDART_INF_F;
                #pragma unroll
                for (int offset = 16; offset; offset >>= 1)
                    maximum = fmaxf(maximum, __shfl_xor_sync(0xffffffff, maximum, offset));
                if (lane == 0) shared[warp] = maximum;
                __syncthreads();
                maximum = -CUDART_INF_F;
                #pragma unroll
                for (int other_warp = 0; other_warp < 8; ++other_warp)
                    maximum = fmaxf(maximum, shared[other_warp]);
                float denominator = 0.0f;
                if (thread < splits) {
                    const float* state = source + thread * 2112;
                    float correction = state[129] > 0 ? __expf(state[128] - maximum) : 0.0f;
                    shared[32 + thread] = correction;
                    denominator = state[129] * correction;
                }
                denominator = warp_sum(denominator);
                if (lane == 0) shared[16 + warp] = denominator;
                __syncthreads();
                float4 numerator = make_float4(0, 0, 0, 0);
                for (int split = warp; split < splits; split += 8) {
                    float4 values = reinterpret_cast<const float4*>(source + split * 2112)[lane];
                    float correction = shared[32 + split];
                    numerator.x += values.x * correction;
                    numerator.y += values.y * correction;
                    numerator.z += values.z * correction;
                    numerator.w += values.w * correction;
                }
                reinterpret_cast<float4*>(shared + 256 + warp * 128)[lane] = numerator;
                __syncthreads();
                if (thread < 128) {
                    float total = 0.0f;
                    denominator = 0.0f;
                    #pragma unroll
                    for (int other_warp = 0; other_warp < 8; ++other_warp) {
                        total += shared[256 + other_warp * 128 + thread];
                        denominator += shared[16 + other_warp];
                    }
                    attention[block * 128 + thread] = total / denominator;
                }
            }
            grid.sync();

            for (int row = block; row < 1024; row += blocks) {
                float sum = 0.0f;
                #pragma unroll
                for (int chunk = 0; chunk < 2; ++chunk) {
                    int column = chunk * 1024 + thread * 4;
                    sum = dot4(weight4(layer.o_proj + row * 2048 + column),
                               reinterpret_cast<float4*>(attention)[column / 4], sum);
                }
                sum = warp_sum(sum);
                if (lane == 0) shared[warp] = sum;
                __syncthreads();
                if (thread == 0) {
                    float total = 0.0f;
                    #pragma unroll
                    for (int other_warp = 0; other_warp < 8; ++other_warp)
                        total += shared[other_warp];
                    residual[row] = total + mix_value(hidden, step_noise, row, mix);
                }
                __syncthreads();
            }
            grid.sync();

            {
                float4 activation[8];
                normalized_post(activation, residual, layer.post_ln);
                for (int row = block * 8 + warp; row < 3072; row += blocks * 8) {
                    float gate = 0.0f;
                    float up = 0.0f;
                    #pragma unroll
                    for (int chunk = 0; chunk < 8; ++chunk) {
                        int column = chunk * 128 + lane * 4;
                        gate = dot4(weight4(layer.gate_proj + row * 1024 + column), activation[chunk], gate);
                        up = dot4(weight4(layer.up_proj + row * 1024 + column), activation[chunk], up);
                    }
                    gate = warp_sum(gate);
                    up = warp_sum(up);
                    if (lane == 0) intermediate[row] = (gate / (1.0f + __expf(-gate))) * up;
                }
            }
            grid.sync();

            for (int row = block; row < 1024; row += blocks) {
                float sum = 0.0f;
                #pragma unroll
                for (int chunk = 0; chunk < 3; ++chunk) {
                    int column = chunk * 1024 + thread * 4;
                    sum = dot4(weight4(layer.down_proj + row * 3072 + column),
                               reinterpret_cast<float4*>(intermediate)[column / 4], sum);
                }
                sum = warp_sum(sum);
                if (lane == 0) shared[warp] = sum;
                __syncthreads();
                if (thread == 0) {
                    float total = 0.0f;
                    #pragma unroll
                    for (int other_warp = 0; other_warp < 8; ++other_warp)
                        total += shared[other_warp];
                    hidden[row] = __float2bfloat16_rn(total + residual[row]);
                }
                __syncthreads();
            }
            grid.sync();
        }
    }
}

int64_t resident_blocks() {
    int device;
    C10_CUDA_CHECK(cudaGetDevice(&device));
    cudaDeviceProp properties;
    C10_CUDA_CHECK(cudaGetDeviceProperties(&properties, device));
    int occupancy;
    C10_CUDA_CHECK(cudaOccupancyMaxActiveBlocksPerMultiprocessor(
        &occupancy, persistent_decode, 256, 0));
    return (min(properties.multiProcessorCount * occupancy, 512) / 8) * 8;
}

void launch_decode(torch::Tensor weights, torch::Tensor caches,
                   torch::Tensor hidden, torch::Tensor noise,
                   torch::Tensor rope, torch::Tensor workspace,
                   int64_t start, int64_t steps, int64_t layers,
                   int64_t capacity, int64_t blocks) {
    auto weights_pointer = reinterpret_cast<const Layer*>(weights.data_ptr<int64_t>());
    auto caches_pointer = reinterpret_cast<bf16**>(caches.data_ptr<int64_t>());
    auto hidden_pointer = reinterpret_cast<bf16*>(hidden.data_ptr<at::BFloat16>());
    auto noise_pointer = reinterpret_cast<const bf16*>(noise.data_ptr<at::BFloat16>());
    auto rope_pointer = rope.data_ptr<float>();
    auto workspace_pointer = workspace.data_ptr<float>();
    int first = start, count = steps, depth = layers, stride = capacity;
    void* arguments[] = {&weights_pointer, &caches_pointer, &hidden_pointer,
                         &noise_pointer, &rope_pointer, &workspace_pointer,
                         &first, &count, &depth, &stride};
    C10_CUDA_CHECK(cudaLaunchCooperativeKernel(
        reinterpret_cast<void*>(persistent_decode), dim3(blocks), dim3(256),
        arguments, 0, at::cuda::getCurrentCUDAStream()));
}
"""


_extension = None


def _cuda_extension():
    global _extension
    if _extension is None:
        os.environ.setdefault("TORCH_CUDA_ARCH_LIST", "12.0")
        os.environ["PATH"] = os.path.join(sys.prefix, "bin") + os.pathsep + os.environ["PATH"]
        _extension = load_inline(
            name="megaqwen_sm120_decode",
            cpp_sources=_CPP,
            cuda_sources=_CUDA,
            functions=["launch_decode", "resident_blocks"],
            extra_cflags=["-O3"],
            extra_cuda_cflags=["-O3", "-lineinfo", "--ptxas-options=-v"],
        )
    return _extension


class _Engine:
    def __init__(self, model):
        self.extension = _cuda_extension()
        self.device = next(model.parameters()).device
        self.signature = tuple(parameter.data_ptr() for parameter in model.parameters())
        self.weights = torch.tensor(self.signature, dtype=torch.int64, device=self.device)
        self.blocks = self.extension.resident_blocks()
        self.workspace = torch.empty(
            10240 + self.blocks * 264, dtype=torch.float32, device=self.device
        )
        inverse = 1.0 / (
            10000 ** (torch.arange(64, dtype=torch.float32, device=self.device) / 64)
        )
        positions = torch.arange(model.max_seq, dtype=torch.float32, device=self.device)
        angles = positions[:, None] * inverse[None, :]
        self.rope = torch.cat((angles.cos(), angles.sin()), dim=1).contiguous()
        self.cache_signature = None
        self.cache_pointers = None

    def bind(self, keys, values):
        signature = tuple(pointer.data_ptr() for pair in zip(keys, values) for pointer in pair)
        if signature != self.cache_signature:
            self.cache_pointers = torch.tensor(signature, dtype=torch.int64, device=self.device)
            self.cache_signature = signature

    def execute(self, model, hidden, noise, keys, values, start):
        self.bind(keys, values)
        self.extension.launch_decode(
            self.weights, self.cache_pointers, hidden, noise, self.rope,
            self.workspace, start, noise.shape[0], model.num_layers,
            model.max_seq, self.blocks,
        )


def _engine(model):
    signature = tuple(parameter.data_ptr() for parameter in model.parameters())
    if model._engine is None or model._engine.signature != signature:
        model._engine = _Engine(model)
    return model._engine


def _noise(count, seed, device):
    generator = torch.Generator(device="cpu").manual_seed(seed)
    return torch.randn(
        (count, HIDDEN), generator=generator, dtype=torch.bfloat16
    ).to(device)


@torch.no_grad()
def prefill(model, ctx_len, seed, device=None):
    if device is not None:
        model = model.to(device)
    device = next(model.parameters()).device
    if ctx_len < 0 or ctx_len > model.max_seq:
        raise ValueError("context does not fit the KV cache")
    engine = _engine(model)
    hidden = _noise(1, seed, device).reshape(HIDDEN)
    keys = [
        torch.zeros((NUM_KV, model.max_seq, HEAD_DIM), dtype=torch.bfloat16, device=device)
        for _ in range(model.num_layers)
    ]
    values = [torch.zeros_like(cache) for cache in keys]
    if ctx_len:
        noise = _noise(ctx_len, seed + 1, device)
        engine.execute(model, hidden, noise, keys, values, 0)
    else:
        engine.bind(keys, values)
    return hidden, keys, values


@torch.no_grad()
def decode_steps(model, hidden, k_caches, v_caches, start_pos, n_steps, seed):
    if start_pos < 0 or n_steps < 0 or start_pos + n_steps > model.max_seq:
        raise ValueError("decode positions do not fit the KV cache")
    result = hidden.clone()
    if n_steps:
        engine = _engine(model)
        noise = _noise(n_steps, seed + 2, result.device)
        engine.execute(model, result, noise, k_caches, v_caches, start_pos)
    return result, k_caches, v_caches


@torch.no_grad()
def run(ctx_len, decode_steps, seed, model=None):
    if model is None:
        model = Model(NUM_LAYERS, max(ctx_len + decode_steps, 512)).cuda().eval()
    hidden, keys, values = prefill(model, ctx_len, seed)
    hidden, keys, values = globals()["decode_steps"](
        model, hidden, keys, values, ctx_len, decode_steps, seed
    )
    return {"last_hidden": hidden}