gemma.cpp/compression/test_util.h

// Copyright 2023 Google LLC
// SPDX-License-Identifier: Apache-2.0
//
// Licensed 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.

#ifndef THIRD_PARTY_GEMMA_CPP_COMPRESSION_TEST_UTIL_H_
#define THIRD_PARTY_GEMMA_CPP_COMPRESSION_TEST_UTIL_H_

#include <stddef.h>
#include <stdint.h>

#include <cmath>

#include "hwy/base.h"

// IWYU pragma: begin_exports
#include "compression/distortion.h"
#include "hwy/stats.h"
#include "hwy/tests/test_util.h"  // RandomState
// IWYU pragma: end_exports

namespace gcpp {

// Returns random Gaussian (mean=0, stddev=1/3 similar to expected weights)
// using the central limit theorem. Avoid std::normal_distribution for
// consistent cross-platform output.
HWY_INLINE double RandomGaussian(hwy::RandomState& rng) {
  uint64_t sum = 0;
  constexpr int kReps = 40;
  for (int rep = 0; rep < kReps; ++rep) {
    sum += hwy::Random32(&rng) & 0xFFFFF;
  }
  const double sum_f =
      static_cast<double>(sum) / static_cast<double>(0xFFFFF * kReps);
  HWY_ASSERT(0.0 <= sum_f && sum_f <= 1.0);
  const double plus_minus_1 = 2.0 * sum_f - 1.0;
  HWY_ASSERT(-1.0 <= plus_minus_1 && plus_minus_1 <= 1.0);
  // Normalize by stddev of sum of uniform random scaled to [-1, 1].
  return plus_minus_1 * std::sqrt(kReps / 3.0);
};

// Returns true if val is inside [min, max].
template <typename T>
static inline bool IsInside(T expected_min, T expected_max, T val) {
  return expected_min <= val && val <= expected_max;
}

template <typename T>
static inline bool IsNear(T expected, T val, T epsilon = T{1E-6}) {
  return IsInside(expected - epsilon, expected + epsilon, val);
}

HWY_INLINE void VerifyGaussian(hwy::Stats& stats) {
  // Inputs are roughly [-1, 1] and symmetric about zero.
  HWY_ASSERT(IsNear(-1.0f, stats.Min(), 0.10f));
  HWY_ASSERT(IsNear(+1.0f, stats.Max(), 0.10f));
  HWY_ASSERT(IsInside(-2E-3, 2E-3, stats.Mean()));
  HWY_ASSERT(IsInside(-0.15, 0.15, stats.Skewness()));
  // Near-Gaussian.
  HWY_ASSERT(IsInside(0.30, 0.35, stats.StandardDeviation()));
  HWY_ASSERT(IsNear(3.0, stats.Kurtosis(), 0.3));
}

}  // namespace gcpp

#endif  // THIRD_PARTY_GEMMA_CPP_COMPRESSION_TEST_UTIL_H_