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8238669: Long.divideUnsigned is extremely slow for certain values (Needs to be Intrinsic)

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Reviewed-by: bpb
This commit is contained in:
Raffaello Giulietti 2020-10-21 16:32:59 +00:00 committed by Brian Burkhalter
parent 365f19c8e1
commit 0efdde188b
2 changed files with 76 additions and 39 deletions
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57
src/java.base/share/classes/java/lang/Long.java
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@ -1668,24 +1668,13 @@ public final class Long extends Number
* @since 1.8 * @since 1.8
*/ */
public static long divideUnsigned(long dividend, long divisor) { public static long divideUnsigned(long dividend, long divisor) {
if (divisor < 0L) { // signed comparison /* See Hacker's Delight (2nd ed), section 9.3 */
// Answer must be 0 or 1 depending on relative magnitude if (divisor >= 0) {
// of dividend and divisor. final long q = (dividend >>> 1) / divisor << 1;
return (compareUnsigned(dividend, divisor)) < 0 ? 0L :1L; final long r = dividend - q * divisor;
} return q + ((r | ~(r - divisor)) >>> (Long.SIZE - 1));
if (dividend > 0) // Both inputs non-negative
return dividend/divisor;
else {
/*
* For simple code, leveraging BigInteger. Longer and faster
* code written directly in terms of operations on longs is
* possible; see "Hacker's Delight" for divide and remainder
* algorithms.
*/
return toUnsignedBigInteger(dividend).
divide(toUnsignedBigInteger(divisor)).longValue();
} }
return (dividend & ~(dividend - divisor)) >>> (Long.SIZE - 1);
} }
/** /**
@ -1701,15 +1690,33 @@ public final class Long extends Number
* @since 1.8 * @since 1.8
*/ */
public static long remainderUnsigned(long dividend, long divisor) { public static long remainderUnsigned(long dividend, long divisor) {
if (dividend > 0 && divisor > 0) { // signed comparisons /* See Hacker's Delight (2nd ed), section 9.3 */
return dividend % divisor; if (divisor >= 0) {
} else { final long q = (dividend >>> 1) / divisor << 1;
if (compareUnsigned(dividend, divisor) < 0) // Avoid explicit check for 0 divisor final long r = dividend - q * divisor;
return dividend; /*
else * Here, 0 <= r < 2 * divisor
return toUnsignedBigInteger(dividend). * (1) When 0 <= r < divisor, the remainder is simply r.
remainder(toUnsignedBigInteger(divisor)).longValue(); * (2) Otherwise the remainder is r - divisor.
*
* In case (1), r - divisor < 0. Applying ~ produces a long with
* sign bit 0, so >> produces 0. The returned value is thus r.
*
* In case (2), a similar reasoning shows that >> produces -1,
* so the returned value is r - divisor.
*/
return r - ((~(r - divisor) >> (Long.SIZE - 1)) & divisor);
} }
/*
* (1) When dividend >= 0, the remainder is dividend.
* (2) Otherwise
* (2.1) When dividend < divisor, the remainder is dividend.
* (2.2) Otherwise the remainder is dividend - divisor
*
* A reasoning similar to the above shows that the returned value
* is as expected.
*/
return dividend - (((dividend & ~(dividend - divisor)) >> (Long.SIZE - 1)) & divisor);
} }
// Bit Twiddling // Bit Twiddling

58
test/jdk/java/lang/Long/Unsigned.java
View File

@ -1,5 +1,5 @@
/* /*
* Copyright (c) 2009, 2012, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 2009, 2020, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -375,24 +375,54 @@ public class Unsigned {
private static int testDivideAndRemainder() { private static int testDivideAndRemainder() {
int errors = 0; int errors = 0;
long MAX_UNSIGNED_INT = Integer.toUnsignedLong(0xffff_ffff); long TWO_31 = 1L << Integer.SIZE - 1;
long TWO_32 = 1L << Integer.SIZE;
long TWO_33 = 1L << Integer.SIZE + 1;
BigInteger NINETEEN = BigInteger.valueOf(19L);
BigInteger TWO_63 = BigInteger.ONE.shiftLeft(Long.SIZE - 1);
BigInteger TWO_64 = BigInteger.ONE.shiftLeft(Long.SIZE);
BigInteger[] inRange = { BigInteger[] inRange = {
BigInteger.valueOf(0L), BigInteger.ZERO,
BigInteger.valueOf(1L), BigInteger.ONE,
BigInteger.valueOf(10L), BigInteger.TEN,
BigInteger.valueOf(2147483646L), // Integer.MAX_VALUE - 1 NINETEEN,
BigInteger.valueOf(2147483647L), // Integer.MAX_VALUE
BigInteger.valueOf(2147483648L), // Integer.MAX_VALUE + 1
BigInteger.valueOf(MAX_UNSIGNED_INT - 1L), BigInteger.valueOf(TWO_31 - 19L),
BigInteger.valueOf(MAX_UNSIGNED_INT), BigInteger.valueOf(TWO_31 - 10L),
BigInteger.valueOf(TWO_31 - 1L),
BigInteger.valueOf(TWO_31),
BigInteger.valueOf(TWO_31 + 1L),
BigInteger.valueOf(TWO_31 + 10L),
BigInteger.valueOf(TWO_31 + 19L),
BigInteger.valueOf(Long.MAX_VALUE - 1L), BigInteger.valueOf(TWO_32 - 19L),
BigInteger.valueOf(Long.MAX_VALUE), BigInteger.valueOf(TWO_32 - 10L),
BigInteger.valueOf(Long.MAX_VALUE).add(BigInteger.ONE), BigInteger.valueOf(TWO_32 - 1L),
BigInteger.valueOf(TWO_32),
BigInteger.valueOf(TWO_32 + 1L),
BigInteger.valueOf(TWO_32 + 10L),
BigInteger.valueOf(TWO_32 - 19L),
TWO.pow(64).subtract(BigInteger.ONE) BigInteger.valueOf(TWO_33 - 19L),
BigInteger.valueOf(TWO_33 - 10L),
BigInteger.valueOf(TWO_33 - 1L),
BigInteger.valueOf(TWO_33),
BigInteger.valueOf(TWO_33 + 1L),
BigInteger.valueOf(TWO_33 + 10L),
BigInteger.valueOf(TWO_33 + 19L),
TWO_63.subtract(NINETEEN),
TWO_63.subtract(BigInteger.TEN),
TWO_63.subtract(BigInteger.ONE),
TWO_63,
TWO_63.add(BigInteger.ONE),
TWO_63.add(BigInteger.TEN),
TWO_63.add(NINETEEN),
TWO_64.subtract(NINETEEN),
TWO_64.subtract(BigInteger.TEN),
TWO_64.subtract(BigInteger.ONE),
}; };
for(BigInteger dividend : inRange) { for(BigInteger dividend : inRange) {