jdk-24/test/jdk/java/lang/StrictMath/ExpTests.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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/*
 * @test
 * @bug 8139688
 * @key randomness
 * @library /test/lib
 * @build jdk.test.lib.RandomFactory
 * @build Tests
 * @build FdlibmTranslit
 * @build ExpTests
 * @run main ExpTests
 * @summary Tests specifically for StrictMath.exp
 */

import jdk.test.lib.RandomFactory;

/**
 * The role of this test is to verify that the FDLIBM exp algorithm is
 * being used by running golden file style tests on values that may
 * vary from one conforming exponential implementation to another.
 */

public class ExpTests {
    private ExpTests(){}

    public static void main(String [] argv) {
        int failures = 0;

        failures += testExp();
        failures += testAgainstTranslit();

        if (failures > 0) {
            System.err.println("Testing the exponential incurred "
                               + failures + " failures.");
            throw new RuntimeException();
        }
    }

    // From the fdlibm source, the overflow threshold in hex is:
    // 0x4086_2E42_FEFA_39EF.
    static final double EXP_OVERFLOW_THRESH  = Double.longBitsToDouble(0x4086_2E42_FEFA_39EFL);

    // From the fdlibm source, the underflow threshold in hex is:
    // 0xc087_4910_D52D_3051L.
    static final double EXP_UNDERFLOW_THRESH = Double.longBitsToDouble(0xc087_4910_D52D_3051L);

    static int testExp() {
        int failures = 0;

        double [][] testCases = {
            // Some of these could be moved to common Math/StrictMath exp testing.
            {Double.NaN,                      Double.NaN},
            {Double.MAX_VALUE,                Double.POSITIVE_INFINITY},
            {Double.POSITIVE_INFINITY,        Double.POSITIVE_INFINITY},
            {Double.NEGATIVE_INFINITY,        +0.0},
            {EXP_OVERFLOW_THRESH,                 0x1.ffff_ffff_fff2ap1023},
            {Math.nextUp(EXP_OVERFLOW_THRESH),    Double.POSITIVE_INFINITY},
            {Math.nextDown(EXP_UNDERFLOW_THRESH), +0.0},
            {EXP_UNDERFLOW_THRESH,                +Double.MIN_VALUE},

            // FDLIBM exp(1.0) does *not* return Math.E
            {1.0,                                  Math.nextUp(Math.E)},
            // Cases observed to differ between FDLIBM and other implementations.
            {+0x1.2e8f20cf3cbe7p+8,                0x1.6a2a59cc78bf8p436},
            {-0x1.49f33ad2c1c58p+9,                0x1.f3ccc815431b6p-953},
            {+0x1.fce66609f7428p+5,                0x1.b59724cb0bc4cp91},
            {-0x1.49f33ad2c1c58p+9,                0x1.f3ccc815431b6p-953},
        };

        for(double[] testCase: testCases)
            failures+=testExpCase(testCase[0], testCase[1]);

        return failures;
    }

    static int testExpCase(double input, double expected) {
        int failures = 0;

        failures+=Tests.test("StrictMath.exp(double)", input,
                             StrictMath.exp(input), expected);
        return failures;
    }

    // Initialize shared random number generator
    private static java.util.Random random = RandomFactory.getRandom();

    /**
     * Test StrictMath.exp against transliteration port of exp.
     */
    private static int testAgainstTranslit() {
        int failures = 0;

        double[] decisionPoints = {
            // Near overflow threshold
            EXP_OVERFLOW_THRESH - 512*Math.ulp(EXP_OVERFLOW_THRESH),

            // Near underflow threshold
            EXP_UNDERFLOW_THRESH - 512*Math.ulp(EXP_UNDERFLOW_THRESH),

            // Straddle algorithm conditional checks
            Double.longBitsToDouble(0x4086_2E42_0000_0000L - 512L),
            Double.longBitsToDouble(0x3fd6_2e42_0000_0000L - 512L),
            Double.longBitsToDouble(0x3FF0_A2B2_0000_0000L - 512L),
            Double.longBitsToDouble(0x3e30_0000_0000_0000L - 512L),

            // Other notable points
            Double.MIN_NORMAL - Math.ulp(Double.MIN_NORMAL)*512,
            -Double.MIN_VALUE*512,
        };

        for (double decisionPoint : decisionPoints) {
            double ulp = Math.ulp(decisionPoint);
            failures += testRange(decisionPoint - 1024*ulp, ulp, 1_024);
        }

        // Try out some random values
        for (int i = 0; i < 100; i++) {
            double x = Tests.createRandomDouble(random);
            failures += testRange(x, Math.ulp(x), 100);
        }

        return failures;
    }

    private static int testRange(double start, double increment, int count) {
        int failures = 0;
        double x = start;
        for (int i = 0; i < count; i++, x += increment) {
            failures += testExpCase(x, FdlibmTranslit.exp(x));
        }
        return failures;
    }
}