/
webidl.js
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/
webidl.js
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'use strict';
const {
MathAbs,
MathMax,
MathMin,
MathPow,
MathSign,
MathTrunc,
NumberIsNaN,
NumberMAX_SAFE_INTEGER,
NumberMIN_SAFE_INTEGER,
} = primordials;
const {
codes: {
ERR_INVALID_ARG_VALUE,
},
} = require('internal/errors');
const { kEmptyObject } = require('internal/util');
// https://webidl.spec.whatwg.org/#abstract-opdef-integerpart
const integerPart = MathTrunc;
/* eslint-disable node-core/non-ascii-character */
// Round x to the nearest integer, choosing the even integer if it lies halfway
// between two, and choosing +0 rather than -0.
// This is different from Math.round, which rounds to the next integer in the
// direction of +β when the fraction portion is exactly 0.5.
/* eslint-enable node-core/non-ascii-character */
function evenRound(x) {
// Convert -0 to +0.
const i = integerPart(x) + 0;
const reminder = MathAbs(x % 1);
const sign = MathSign(i);
if (reminder === 0.5) {
return i % 2 === 0 ? i : i + sign;
}
const r = reminder < 0.5 ? i : i + sign;
// Convert -0 to +0.
if (r === 0) {
return 0;
}
return r;
}
function pow2(exponent) {
// << operates on 32 bit signed integers.
if (exponent < 31) {
return 1 << exponent;
}
if (exponent === 31) {
return 0x8000_0000;
}
if (exponent === 32) {
return 0x1_0000_0000;
}
return MathPow(2, exponent);
}
// https://tc39.es/ecma262/#eqn-modulo
// The notation βx modulo yβ computes a value k of the same sign as y.
function modulo(x, y) {
const r = x % y;
// Convert -0 to +0.
if (r === 0) {
return 0;
}
return r;
}
// https://webidl.spec.whatwg.org/#abstract-opdef-converttoint
function convertToInt(name, value, bitLength, options = kEmptyObject) {
const { signed = false, enforceRange = false, clamp = false } = options;
let upperBound;
let lowerBound;
// 1. If bitLength is 64, then:
if (bitLength === 64) {
// 1.1. Let upperBound be 2^53 β 1.
upperBound = NumberMAX_SAFE_INTEGER;
// 1.2. If signedness is "unsigned", then let lowerBound be 0.
// 1.3. Otherwise let lowerBound be β2^53 + 1.
lowerBound = !signed ? 0 : NumberMIN_SAFE_INTEGER;
} else if (!signed) {
// 2. Otherwise, if signedness is "unsigned", then:
// 2.1. Let lowerBound be 0.
// 2.2. Let upperBound be 2^bitLength β 1.
lowerBound = 0;
upperBound = pow2(bitLength) - 1;
} else {
// 3. Otherwise:
// 3.1. Let lowerBound be -2^(bitLength β 1).
// 3.2. Let upperBound be 2^(bitLength β 1) β 1.
lowerBound = -pow2(bitLength - 1);
upperBound = pow2(bitLength - 1) - 1;
}
// 4. Let x be ? ToNumber(V).
let x = +value;
// 5. If x is β0, then set x to +0.
if (x === 0) {
x = 0;
}
// 6. If the conversion is to an IDL type associated with the [EnforceRange]
// extended attribute, then:
if (enforceRange) {
// 6.1. If x is NaN, +β, or ββ, then throw a TypeError.
if (NumberIsNaN(x) || x === Infinity || x === -Infinity) {
throw new ERR_INVALID_ARG_VALUE(name, x);
}
// 6.2. Set x to IntegerPart(x).
x = integerPart(x);
// 6.3. If x < lowerBound or x > upperBound, then throw a TypeError.
if (x < lowerBound || x > upperBound) {
throw new ERR_INVALID_ARG_VALUE(name, x);
}
// 6.4. Return x.
return x;
}
// 7. If x is not NaN and the conversion is to an IDL type associated with
// the [Clamp] extended attribute, then:
if (clamp && !NumberIsNaN(x)) {
// 7.1. Set x to min(max(x, lowerBound), upperBound).
x = MathMin(MathMax(x, lowerBound), upperBound);
// 7.2. Round x to the nearest integer, choosing the even integer if it
// lies halfway between two, and choosing +0 rather than β0.
x = evenRound(x);
// 7.3. Return x.
return x;
}
// 8. If x is NaN, +0, +β, or ββ, then return +0.
if (NumberIsNaN(x) || x === 0 || x === Infinity || x === -Infinity) {
return 0;
}
// 9. Set x to IntegerPart(x).
x = integerPart(x);
// 10. Set x to x modulo 2^bitLength.
x = modulo(x, pow2(bitLength));
// 11. If signedness is "signed" and x β₯ 2^(bitLength β 1), then return x β
// 2^bitLength.
if (signed && x >= pow2(bitLength - 1)) {
return x - pow2(bitLength);
}
// 12. Otherwise, return x.
return x;
}
module.exports = {
convertToInt,
evenRound,
};