log4j/src/testcases/org/apache/poi/ss/formula/eval/TestMinusZeroResult.java

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package org.apache.poi.ss.formula.eval;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;

import org.apache.poi.ss.formula.functions.Function;
import org.junit.jupiter.api.Test;

/**
 * IEEE 754 defines a quantity '-0.0' which is distinct from '0.0'.
 * Negative zero is not easy to observe in Excel, since it is usually converted to 0.0.
 * (Note - the results of XLL add-in functions don't seem to be converted, so they are one
 * reliable avenue to observe Excel's treatment of '-0.0' as an operand.)
 * <p>
 * POI attempts to emulate Excel faithfully, so this class tests
 * two aspects of '-0.0' in formula evaluation:
 * <ol>
 * <li>For most operation results '-0.0' is converted to '0.0'.</li>
 * <li>Comparison operators have slightly different rules regarding '-0.0'.</li>
 * </ol>
 */
final class TestMinusZeroResult {
	private static final double MINUS_ZERO = -0.0;

	@Test
	void testSimpleOperators() {

		// unary plus is a no-op
		checkEval(MINUS_ZERO, UnaryPlusEval.instance, MINUS_ZERO);

		// most simple operators convert -0.0 to +0.0
		checkEval(0.0, EvalInstances.UnaryMinus, 0.0);
		checkEval(0.0, EvalInstances.Percent, MINUS_ZERO);
		checkEval(0.0, EvalInstances.Multiply, MINUS_ZERO, 1.0);
		checkEval(0.0, EvalInstances.Divide, MINUS_ZERO, 1.0);
		checkEval(0.0, EvalInstances.Power, MINUS_ZERO, 1.0);

		// but SubtractEval does not convert -0.0, so '-' and '+' work like java
		checkEval(MINUS_ZERO, EvalInstances.Subtract, MINUS_ZERO, 0.0); // this is the main point of bug 47198
		checkEval(0.0, EvalInstances.Add, MINUS_ZERO, 0.0);
	}

	/**
	 * These results are hard to see in Excel (since -0.0 is usually converted to +0.0 before it
	 * gets to the comparison operator)
	 */
	@Test
	void testComparisonOperators() {
		checkEval(false, EvalInstances.Equal, 0.0, MINUS_ZERO);
		checkEval(true, EvalInstances.GreaterThan, 0.0, MINUS_ZERO);
		checkEval(true, EvalInstances.LessThan, MINUS_ZERO, 0.0);
	}

	@Test
	void testTextRendering() {
		confirmTextRendering(MINUS_ZERO);
		// sub-normal negative numbers also display as '-0'
		confirmTextRendering(Double.longBitsToDouble(0x8000100020003000L));
	}

	/**
	 * Uses {@link ConcatEval} to force number-to-text conversion
	 */
	private static void confirmTextRendering(double d) {
		ValueEval[] args = { StringEval.EMPTY_INSTANCE, new NumberEval(d), };
		StringEval se = (StringEval) EvalInstances.Concat.evaluate(args, -1, (short)-1);
		String result = se.getStringValue();
		assertEquals("-0", result);
	}

	private static void checkEval(double expectedResult, Function instance, double... dArgs) {
		NumberEval result = (NumberEval) evaluate(instance, dArgs);
		assertDouble(expectedResult, result.getNumberValue());
	}
	private static void checkEval(boolean expectedResult, Function instance, double... dArgs) {
		BoolEval result = (BoolEval) evaluate(instance, dArgs);
		assertEquals(expectedResult, result.getBooleanValue());
	}
	private static ValueEval evaluate(Function instance, double... dArgs) {
		ValueEval[] evalArgs;
		evalArgs = new ValueEval[dArgs.length];
		for (int i = 0; i < evalArgs.length; i++) {
			evalArgs[i] = new NumberEval(dArgs[i]);
		}
        return instance.evaluate(evalArgs, -1, (short)-1);
	}

	/**
	 * Not really a POI test - just shows similar behaviour of '-0.0' in Java.
	 */
	@Test
	void testJava() {
		assertEquals(0x8000000000000000L, Double.doubleToLongBits(MINUS_ZERO));

		// The simple operators consider all zeros to be the same
		//noinspection SimplifiableJUnitAssertion,ConstantConditions
		assertTrue(MINUS_ZERO == MINUS_ZERO);
		//noinspection SimplifiableJUnitAssertion,ConstantConditions
		assertTrue(MINUS_ZERO == +0.0);
		//noinspection ConstantConditions
		assertFalse(MINUS_ZERO < +0.0);

		// Double.compare() considers them different
		assertTrue(Double.compare(MINUS_ZERO, +0.0) < 0);

		// multiplying zero by any negative quantity yields minus zero
		assertDouble(MINUS_ZERO, 0.0*-1);
		assertDouble(MINUS_ZERO, 0.0*-1e300);
		assertDouble(MINUS_ZERO, 0.0*-1e-300);

		// minus zero can be produced as a result of underflow
		assertDouble(MINUS_ZERO, -1e-300 / 1e100);

		// multiplying or dividing minus zero by a positive quantity yields minus zero
		assertDouble(MINUS_ZERO, MINUS_ZERO * 1.0);
		assertDouble(MINUS_ZERO, MINUS_ZERO / 1.0);

		// subtracting positive zero gives minus zero
		assertDouble(MINUS_ZERO, MINUS_ZERO - 0.0);
		// BUT adding positive zero gives positive zero
		assertDouble(0.0, MINUS_ZERO + 0.0);  // <<----
	}

	/**
	 * Just so there is no ambiguity.  The two double values have to be exactly equal
	 */
	private static void assertDouble(double a, double b) {
		long bitsA = Double.doubleToLongBits(a);
		long bitsB = Double.doubleToLongBits(b);
		assertEquals(bitsA, bitsB);
	}
}