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8188044: We need Math.unsignedMultiplyHigh
Reviewed-by: rriggs, aph, darcy
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Brian Burkhalter committed Jul 2, 2021
1 parent 3d84398 commit ca4bea466581217cae2278c98c0fdc568c043818
@@ -1156,6 +1156,7 @@ public static long multiplyFull(int x, int y) {
* @param x the first value
* @param y the second value
* @return the result
* @see #unsignedMultiplyHigh
* @since 9
*/
@IntrinsicCandidate
@@ -1187,6 +1188,24 @@ public static long multiplyHigh(long x, long y) {
}
}

/**
* Returns as a {@code long} the most significant 64 bits of the unsigned
* 128-bit product of two unsigned 64-bit factors.
*
* @param x the first value
* @param y the second value
* @return the result
* @see #multiplyHigh
* @since 18
*/
public static long unsignedMultiplyHigh(long x, long y) {
// Compute via multiplyHigh() to leverage the intrinsic
long result = Math.multiplyHigh(x, y);
result += (y & (x >> 63)); // equivalent to `if (x < 0) result += y;`
result += (x & (y >> 63)); // equivalent to `if (y < 0) result += x;`
return result;
}

/**
* Returns the largest (closest to positive infinity)
* {@code int} value that is less than or equal to the algebraic quotient.
@@ -982,13 +982,29 @@ public static long multiplyFull(int x, int y) {
* @param x the first value
* @param y the second value
* @return the result
* @see #unsignedMultiplyHigh
* @see Math#multiplyHigh(long,long)
* @since 9
*/
public static long multiplyHigh(long x, long y) {
return Math.multiplyHigh(x, y);
}

/**
* Returns as a {@code long} the most significant 64 bits of the unsigned
* 128-bit product of two unsigned 64-bit factors.
*
* @param x the first value
* @param y the second value
* @return the result
* @see #multiplyHigh
* @see Math#unsignedMultiplyHigh(long,long)
* @since 18
*/
public static long unsignedMultiplyHigh(long x, long y) {
return Math.unsignedMultiplyHigh(x, y);
}

/**
* Returns the largest (closest to positive infinity)
* {@code int} value that is less than or equal to the algebraic quotient.
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2016, 2021, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -26,12 +26,13 @@
* @library /test/lib
* @build jdk.test.lib.RandomFactory
* @run main MultiplicationTests
* @bug 5100935
* @bug 5100935 8188044
* @summary Tests for multiplication methods (use -Dseed=X to set PRNG seed)
* @key randomness
*/

import java.math.BigInteger;
import java.util.function.BiFunction;
import jdk.test.lib.RandomFactory;

public class MultiplicationTests {
@@ -49,10 +50,25 @@ private static long multiplyHighBigInt(long x, long y) {
.shiftRight(64).longValue();
}

// Check Math.multiplyHigh(x,y) against multiplyHighBigInt(x,y)
private static boolean check(long x, long y) {
long p1 = multiplyHighBigInt(x, y);
long p2 = Math.multiplyHigh(x, y);
// Calculate high 64 bits of unsigned 128 product using signed multiply
private static long unsignedMultiplyHigh(long x, long y) {
long x0 = x & 0xffffffffL;
long x1 = x >>> 32;
long y0 = y & 0xffffffffL;
long y1 = y >>> 32;

long t = x1 * y0 + ((x0 * y0) >>> 32);
long z0 = x0 * y1 + (t & 0xffffffffL);
long z1 = t >>> 32;

return x1 * y1 + z1 + (z0 >>> 32);
}

// Compare results of two functions for a pair of values
private static boolean check(BiFunction<Long,Long,Long> reference,
BiFunction<Long,Long,Long> multiply, long x, long y) {
long p1 = reference.apply(x, y);
long p2 = multiply.apply(x, y);
if (p1 != p2) {
System.err.printf("Error - x:%d y:%d p1:%d p2:%d\n", x, y, p1, p2);
return false;
@@ -61,7 +77,19 @@ private static boolean check(long x, long y) {
}
}

private static int testMultiplyHigh() {
// Check Math.multiplyHigh(x,y) against multiplyHighBigInt(x,y)
private static boolean checkSigned(long x, long y) {
return check((a,b) -> multiplyHighBigInt(a,b),
(a,b) -> Math.multiplyHigh(a, b), x, y);
}

// Check Math.unsignedMultiplyHigh(x,y) against unsignedMultiplyHigh(x,y)
private static boolean checkUnsigned(long x, long y) {
return check((a,b) -> unsignedMultiplyHigh(a,b),
(a,b) -> Math.unsignedMultiplyHigh(a, b), x, y);
}

private static int test(BiFunction<Long,Long,Boolean> chk) {
int failures = 0;

// check some boundary cases
@@ -84,23 +112,31 @@ private static int testMultiplyHigh() {
};

for (long[] xy : v) {
if(!check(xy[0], xy[1])) {
if(!chk.apply(xy[0], xy[1])) {
failures++;
}
}

// check some random values
for (int i = 0; i < COUNT; i++) {
if (!check(rnd.nextLong(), rnd.nextLong())) {
if (!chk.apply(rnd.nextLong(), rnd.nextLong())) {
failures++;
}
}

return failures;
}

private static int testMultiplyHigh() {
return test((x,y) -> checkSigned(x,y));
}

private static int testUnsignedMultiplyHigh() {
return test((x,y) -> checkUnsigned(x,y));
}

public static void main(String argv[]) {
int failures = testMultiplyHigh();
int failures = testMultiplyHigh() + testUnsignedMultiplyHigh();

if (failures > 0) {
System.err.println("Multiplication testing encountered "

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