/*
    * 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.
   */
  package org.apache.commons.numbers.core;
  
  import java.math.BigDecimal;
  import org.junit.jupiter.api.Assertions;
  import org.junit.jupiter.api.Test;
  
  /**
   * Test cases for the {@link ExtendedPrecision} class.
   */
  class ExtendedPrecisionTest {
      @Test
      void testSplitAssumptions() {
          // The multiplier used to split the double value into high and low parts.
          final double scale = (1 << 27) + 1;
          // The upper limit above which a number may overflow during the split into a high part.
          final double limit = 0x1.0p996;
          Assertions.assertTrue(Double.isFinite(limit * scale));
          Assertions.assertTrue(Double.isFinite(-limit * scale));
          // Cannot make the limit the next power up
          Assertions.assertEquals(Double.POSITIVE_INFINITY, limit * 2 * scale);
          Assertions.assertEquals(Double.NEGATIVE_INFINITY, -limit * 2 * scale);
          // Check the level for the safe upper limit of the exponent of the sum of the absolute
          // components of the product
          Assertions.assertTrue(Math.getExponent(2 * Math.sqrt(Double.MAX_VALUE)) - 2 > 508);
      }
  
      @Test
      void testHighPartUnscaled() {
          Assertions.assertEquals(Double.NaN, ExtendedPrecision.highPartUnscaled(Double.POSITIVE_INFINITY));
          Assertions.assertEquals(Double.NaN, ExtendedPrecision.highPartUnscaled(Double.NEGATIVE_INFINITY));
          Assertions.assertEquals(Double.NaN, ExtendedPrecision.highPartUnscaled(Double.NaN));
          // Large finite numbers will overflow during the split
          Assertions.assertEquals(Double.NaN, ExtendedPrecision.highPartUnscaled(Double.MAX_VALUE));
          Assertions.assertEquals(Double.NaN, ExtendedPrecision.highPartUnscaled(-Double.MAX_VALUE));
      }
  
      /**
       * Test {@link ExtendedPrecision#productLow(double, double, double)} computes the same
       * result as JDK 9 Math.fma(x, y, -x * y) for edge cases.
       */
      @Test
      void testProductLow() {
          assertProductLow(0.0, 1.0, Math.nextDown(Double.MIN_NORMAL));
          assertProductLow(0.0, -1.0, Math.nextDown(Double.MIN_NORMAL));
          assertProductLow(Double.NaN, 1.0, Double.POSITIVE_INFINITY);
          assertProductLow(Double.NaN, 1.0, Double.NEGATIVE_INFINITY);
          assertProductLow(Double.NaN, 1.0, Double.NaN);
          assertProductLow(0.0, 1.0, Double.MAX_VALUE);
          assertProductLow(Double.NaN, 2.0, Double.MAX_VALUE);
      }
  
      private static void assertProductLow(double expected, double x, double y) {
          // Requires a delta of 0.0 to assert -0.0 == 0.0
          Assertions.assertEquals(expected, ExtendedPrecision.productLow(x, y, x * y), 0.0);
      }
  
      @Test
      void testIsNotNormal() {
          for (double a : new double[] {Double.MAX_VALUE, 1.0, Double.MIN_NORMAL}) {
              Assertions.assertFalse(ExtendedPrecision.isNotNormal(a));
              Assertions.assertFalse(ExtendedPrecision.isNotNormal(-a));
          }
          for (double a : new double[] {Double.POSITIVE_INFINITY, 0.0,
                                        Math.nextDown(Double.MIN_NORMAL), Double.NaN}) {
              Assertions.assertTrue(ExtendedPrecision.isNotNormal(a));
              Assertions.assertTrue(ExtendedPrecision.isNotNormal(-a));
          }
      }
  
      /**
       * This demonstrates splitting a sub normal number with no information in the upper 26 bits
       * of the mantissa.
       */
      @Test
      void testSubNormalSplit() {
          final double a = Double.longBitsToDouble(1L << 25);
  
          // A split using masking of the mantissa bits computes the high part incorrectly
          final double hi1 = Double.longBitsToDouble(Double.doubleToRawLongBits(a) & ((-1L) << 27));
          final double lo1 = a - hi1;
          Assertions.assertEquals(0, hi1);
          Assertions.assertEquals(a, lo1);
          Assertions.assertFalse(Math.abs(hi1) > Math.abs(lo1));
 
         // Dekker's split
         final double hi2 = ExtendedPrecision.highPartUnscaled(a);
         final double lo2 = a - hi2;
         Assertions.assertEquals(a, hi2);
         Assertions.assertEquals(0, lo2);
 
         Assertions.assertTrue(Math.abs(hi2) > Math.abs(lo2));
     }
 
     @Test
     void testSquareLowUnscaled() {
         assertSquareLowUnscaled(0.0, 1.0);
         assertSquareLowUnscaled(0.0, -1.0);
         final double expected = new BigDecimal(Math.PI).pow(2)
                 .subtract(new BigDecimal(Math.PI * Math.PI)).doubleValue();
         assertSquareLowUnscaled(expected, Math.PI);
 
         assertSquareLowUnscaled(Double.NaN, Double.POSITIVE_INFINITY);
         assertSquareLowUnscaled(Double.NaN, Double.NEGATIVE_INFINITY);
         assertSquareLowUnscaled(Double.NaN, Double.NaN);
         assertSquareLowUnscaled(Double.NaN, Double.MAX_VALUE);
     }
 
     private static void assertSquareLowUnscaled(final double expected, final double x) {
         Assertions.assertEquals(expected, ExtendedPrecision.squareLowUnscaled(x, x * x));
     }
 }