com.google.javascript.jscomp.base.JSCompDoubles Maven / Gradle / Ivy
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/*
* Copyright 2020 The Closure Compiler Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.javascript.jscomp.base;
import static com.google.common.base.Preconditions.checkState;
/** Basic double functions used by JSComp. */
public final class JSCompDoubles {
/**
* Can a 32 bit int exactly represent `x`?
*
* Many double values are not exact integers. Many that are integers are too large to fit into
* a Java int.
*
*
This function does not guarantee that a value can be round-tripped from double to int to
* double and have an identical bit pattern. Notably, 0.0 and -0.0 both represent exactly 0.
*/
public static boolean isExactInt32(double x) {
return !Double.isNaN(x) && ((double) ((int) x)) == x;
}
/**
* Can a 64 bit int exactly represent `x`?
*
*
Many double values are not exact integers. Many that are integers are too large to fit into
* a Java long.
*
*
This function does not guarantee that a value can be round-tripped from double to long to
* double and have an identical bit pattern. Notably, 0.0 and -0.0 both represent exactly 0.
*/
public static boolean isExactInt64(double x) {
return !Double.isNaN(x) && ((double) ((long) x)) == x;
}
/**
* Does `x` exactly represent an value with no fractional part?
*
*
The value may be too large to fit in a primitive integral type, such as long.
*
*
Returns false for NaN and Infinity.
*
*
This should behave identically to Guava {@code DoubleMath.isMathematicalInteger} but is J2CL
* compatible.
*/
public static boolean isMathematicalInteger(double x) {
return x % 1.0 == 0.0;
}
/**
* Does `x` have precision down to the "ones column"?
*
*
A double can hold exact integer values that are very large, but to do so it may loose
* precision at the scale of "ones". That is "largeDouble + 1.0 == largeDouble" may be true.
*
*
Returns false for NaN and Infinity.
*/
public static boolean isAtLeastIntegerPrecision(double x) {
// It's possible for a JVM to use floating-point values with more than 53 bits of precision,
// but we have to be conservative.
return Math.abs(x) < POW_2_53;
}
/**
* Does `x` carry a negative sign?
*
*
Because -0.0 == 0.0, it is not enough to check `x < 0.0` to determine if a double is
* negative. This function identifies the -0.0 case.
*
* @throws if passed NaN since NaNs are neither positive nor negative.
*/
public static boolean isNegative(double x) {
checkState(!Double.isNaN(x));
return Double.compare(0.0, x) > 0;
}
/**
* Does `x` not carry a negative sign?
*
*
Because -0.0 == 0.0, it is not enough to check `x < 0.0` to determine if a double is
* negative. This function identifies the -0.0 case.
*
* @throws if passed NaN since NaNs are neither positive nor negative.
*/
public static boolean isPositive(double x) {
return !isNegative(x);
}
/** Is `x` positive or negative zero? */
public static boolean isEitherZero(double x) {
return x == 0.0;
}
/**
* The ECMAScript ToInt32 abstract operation.
*
*
See https://262.ecma-international.org/5.1/#sec-9.5
*/
public static int ecmascriptToInt32(double number) {
// Fast path for most common case. Also covers -0.0
if (isExactInt32(number)) {
return (int) number;
}
// Step 2
if (Double.isNaN(number) || Double.isInfinite(number)) {
return 0;
}
// Step 3
double posInt = (number >= 0) ? Math.floor(number) : Math.ceil(number);
/**
* Step 4
*
*
Afer modding, the value must fit into a long, but not necessarily an int.
*
*
If value produced by modding is negative, the spec says to add 2^32 so that `int32bit` is
* positive. However, that addition doesn't affect the trailing 32 bits of the `int32bit`, which
* are the only ones that matter.
*/
long int32bit = (long) (posInt % POW_2_32);
/**
* Step 5
*
*
The instructions in the spec are equivalent to interpreting the last 32 bits of `int32bit`
* as a 2s-compliment integer, which is exactly the representation Java uses for int.
*/
return (int) int32bit;
}
/**
* The ECMAScript ToUint32 abstract operation.
*
*
Java has no uint types, so the caller must remember to treat the returned bits as a uint.
*
*
See https://262.ecma-international.org/5.1/#sec-9.6
*/
public static int ecmascriptToUint32(double number) {
return ecmascriptToInt32(number);
}
private static final double POW_2_32 = Math.pow(2, 32);
private static final double POW_2_53 = Math.pow(2, 53);
private JSCompDoubles() {
throw new AssertionError();
}
}