src/flowgraph/IntegerRatio.cpp

/*
 * Copyright 2019 The Android Open Source Project
 *
 * 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.
 */

#include <vector>

#include "IntegerRatio.h"

using namespace flowgraph;

const std::vector<int>  IntegerRatio::kPrimes{
        2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41,
        43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97,
        101, 103, 107, 109, 113, 127, 131, 137, 139, 149,
        151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199};

void IntegerRatio::reduce() {
    int32_t factoredTop = mNumerator;
    int32_t factoredBottom = mDenominator;
    bool downToOne = false;
    for (int prime : kPrimes) {
        if (mNumerator < prime
            || mDenominator < prime
            || downToOne)
            break;
        int topCount = 0;
        while (true) {
            int top = factoredTop / prime;
            if (factoredTop == top * prime) {
                topCount++;
                factoredTop = top;
                downToOne |= top == 1;
            } else {
                break;
            }
        }
        int bottomCount = 0;
        while (true) {
            int bottom = factoredBottom / prime;
            if (factoredBottom == bottom * prime) {
                bottomCount++;
                factoredBottom = bottom;
                downToOne |= bottom == 1;
            } else {
                break;
            }
        }

        int commonCount = std::min(topCount, bottomCount);
        while (commonCount--) {
            mNumerator /= prime;
            mDenominator /= prime;
        }
    }
}