ryankert01 commented on code in PR #868: URL: https://github.com/apache/mahout/pull/868#discussion_r2719980290
########## qdp/qdp-kernels/src/iqp.cu: ########## @@ -0,0 +1,232 @@ +// +// Licensed to the Apache Software Foundation (ASF) under one or more +// contributor license agreements. See the NOTICE file distributed with +// this work for additional information regarding copyright ownership. +// The ASF licenses this file to You under the Apache License, Version 2.0 +// (the "License"); you may not use this file except in compliance with +// the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +// IQP (Instantaneous Quantum Polynomial) Encoding CUDA Kernels +// +// Creates entangled quantum states via diagonal phase gates: +// |psi> = H^n * U_phase(data) * H^n |0>^n +// +// The amplitude for basis state |z> is: +// amplitude[z] = (1/2^n) * sum_x exp(i*theta(x)) * (-1)^popcount(x AND z) +// +// Two variants: +// - enable_zz=0: theta(x) = sum_i x_i * data_i (n parameters) +// - enable_zz=1: theta(x) = sum_i x_i * data_i + sum_{i<j} x_i * x_j * data_ij +// (n + n*(n-1)/2 parameters) + +#include <cuda_runtime.h> +#include <cuComplex.h> +#include <math.h> + +// Compute phase theta(x) for a given basis state x +__device__ double compute_phase( + const double* __restrict__ data, + size_t x, + unsigned int num_qubits, + int enable_zz +) { + double phase = 0.0; + + // Single-qubit Z terms: sum_i x_i * data[i] + for (unsigned int i = 0; i < num_qubits; ++i) { + if ((x >> i) & 1U) { + phase += data[i]; + } + } + + // Two-qubit ZZ terms (if enabled): sum_{i<j} x_i * x_j * data[n + pair_index] + if (enable_zz) { + unsigned int pair_idx = num_qubits; + for (unsigned int i = 0; i < num_qubits; ++i) { + for (unsigned int j = i + 1; j < num_qubits; ++j) { + if (((x >> i) & 1U) && ((x >> j) & 1U)) { + phase += data[pair_idx]; + } + pair_idx++; + } + } + } + + return phase; +} + +__global__ void iqp_encode_kernel( + const double* __restrict__ data, + cuDoubleComplex* __restrict__ state, + size_t state_len, + unsigned int num_qubits, + int enable_zz +) { + size_t z = blockIdx.x * blockDim.x + threadIdx.x; + if (z >= state_len) return; + + double real_sum = 0.0; + double imag_sum = 0.0; + + // Sum over all input basis states x + for (size_t x = 0; x < state_len; ++x) { + double phase = compute_phase(data, x, num_qubits, enable_zz); + + // Compute (-1)^{popcount(x AND z)} using __popcll intrinsic + int parity = __popcll(x & z) & 1; + double sign = (parity == 0) ? 1.0 : -1.0; + + // Accumulate: sign * exp(i*phase) = sign * (cos(phase) + i*sin(phase)) + double cos_phase, sin_phase; + sincos(phase, &sin_phase, &cos_phase); + real_sum += sign * cos_phase; + imag_sum += sign * sin_phase; + } + + // Normalize by 1/2^n (state_len = 2^n) + double norm = 1.0 / (double)state_len; + state[z] = make_cuDoubleComplex(real_sum * norm, imag_sum * norm); +} + +__global__ void iqp_encode_batch_kernel( + const double* __restrict__ data_batch, + cuDoubleComplex* __restrict__ state_batch, + size_t num_samples, + size_t state_len, + unsigned int num_qubits, + unsigned int data_len, + int enable_zz +) { + const size_t total_elements = num_samples * state_len; + const size_t stride = gridDim.x * blockDim.x; + const size_t state_mask = state_len - 1; + + for (size_t global_idx = blockIdx.x * blockDim.x + threadIdx.x; + global_idx < total_elements; + global_idx += stride) { + const size_t sample_idx = global_idx >> num_qubits; + const size_t z = global_idx & state_mask; + const double* data = data_batch + sample_idx * data_len; + + double real_sum = 0.0; + double imag_sum = 0.0; + + // Sum over all input basis states x + for (size_t x = 0; x < state_len; ++x) { + double phase = compute_phase(data, x, num_qubits, enable_zz); + + // Compute (-1)^{popcount(x AND z)} + int parity = __popcll(x & z) & 1; + double sign = (parity == 0) ? 1.0 : -1.0; + + double cos_phase, sin_phase; + sincos(phase, &sin_phase, &cos_phase); + real_sum += sign * cos_phase; + imag_sum += sign * sin_phase; + } + + double norm = 1.0 / (double)state_len; + state_batch[global_idx] = make_cuDoubleComplex(real_sum * norm, imag_sum * norm); + } +} + +extern "C" { + +/// Launch IQP encoding kernel +/// +/// # Arguments +/// * data_d - Device pointer to encoding parameters +/// * state_d - Device pointer to output state vector +/// * state_len - Target state vector size (2^num_qubits) +/// * num_qubits - Number of qubits +/// * enable_zz - 0 for Z-only, 1 for full ZZ interactions +/// * stream - CUDA stream for async execution (nullptr = default stream) +/// +/// # Returns +/// CUDA error code (0 = cudaSuccess) +int launch_iqp_encode( + const double* data_d, + void* state_d, + size_t state_len, + unsigned int num_qubits, + int enable_zz, + cudaStream_t stream +) { + if (state_len == 0 || num_qubits == 0) { + return cudaErrorInvalidValue; + } + + cuDoubleComplex* state_complex_d = static_cast<cuDoubleComplex*>(state_d); + + const int blockSize = 256; Review Comment: Good catch! -- This is an automated message from the Apache Git Service. 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