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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
*/
public static long divideUnsigned(long dividend, long divisor) {
if (divisor < 0L) { // signed comparison
// Answer must be 0 or 1 depending on relative magnitude
// of dividend and divisor.
return (compareUnsigned(dividend, divisor)) < 0 ? 0L :1L;
}
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();
/* See Hacker's Delight (2nd ed), section 9.3 */
if (divisor >= 0) {
final long q = (dividend >>> 1) / divisor << 1;
final long r = dividend - q * divisor;
return q + ((r | ~(r - divisor)) >>> (Long.SIZE - 1));
}
return (dividend & ~(dividend - divisor)) >>> (Long.SIZE - 1);
}
/**
@ -1701,15 +1690,33 @@ public final class Long extends Number
* @since 1.8
*/
public static long remainderUnsigned(long dividend, long divisor) {
if (dividend > 0 && divisor > 0) { // signed comparisons
return dividend % divisor;
} else {
if (compareUnsigned(dividend, divisor) < 0) // Avoid explicit check for 0 divisor
return dividend;
else
return toUnsignedBigInteger(dividend).
remainder(toUnsignedBigInteger(divisor)).longValue();
/* See Hacker's Delight (2nd ed), section 9.3 */
if (divisor >= 0) {
final long q = (dividend >>> 1) / divisor << 1;
final long r = dividend - q * divisor;
/*
* Here, 0 <= r < 2 * divisor
* (1) When 0 <= r < divisor, the remainder is simply r.
* (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