hexo/node_modules/es-abstract/2017/RawBytesToNumber.js

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2023-10-03 11:14:36 +08:00
'use strict';
var GetIntrinsic = require('get-intrinsic');
var callBound = require('call-bind/callBound');
var $pow = GetIntrinsic('%Math.pow%');
var $RangeError = GetIntrinsic('%RangeError%');
var $TypeError = GetIntrinsic('%TypeError%');
var $charAt = callBound('String.prototype.charAt');
var $reverse = callBound('Array.prototype.reverse');
var $slice = callBound('Array.prototype.slice');
var hasOwnProperty = require('./HasOwnProperty');
var IsArray = require('./IsArray');
var Type = require('./Type');
var every = require('../helpers/every');
var isByteValue = require('../helpers/isByteValue');
var keys = require('object-keys');
// https://262.ecma-international.org/8.0/#table-50
var TypeToSizes = {
__proto__: null,
Int8: 1,
Uint8: 1,
Uint8C: 1,
Int16: 2,
Uint16: 2,
Int32: 4,
Uint32: 4,
Float32: 4,
Float64: 8
};
// https://262.ecma-international.org/8.0/#sec-rawbytestonumber
module.exports = function RawBytesToNumber(type, rawBytes, isLittleEndian) {
if (typeof type !== 'string' || !hasOwnProperty(TypeToSizes, type)) {
throw new $TypeError('Assertion failed: `type` must be a TypedArray element type: ' + keys(TypeToSizes));
}
if (!IsArray(rawBytes) || !every(rawBytes, isByteValue)) {
throw new $TypeError('Assertion failed: `rawBytes` must be an Array of bytes');
}
if (Type(isLittleEndian) !== 'Boolean') {
throw new $TypeError('Assertion failed: `isLittleEndian` must be a Boolean');
}
var elementSize = TypeToSizes[type]; // step 1
if (rawBytes.length !== elementSize) {
// this assertion is not in the spec, but it'd be an editorial error if it were ever violated
throw new $RangeError('Assertion failed: `rawBytes` must have a length of ' + elementSize + ' for type ' + type);
}
// eslint-disable-next-line no-param-reassign
rawBytes = $slice(rawBytes, 0, elementSize);
if (!isLittleEndian) {
// eslint-disable-next-line no-param-reassign
rawBytes = $reverse(rawBytes); // step 2
}
/* eslint no-redeclare: 1 */
if (type === 'Float32') { // step 3
/*
Let value be the byte elements of rawBytes concatenated and interpreted as a little-endian bit string encoding of an IEEE 754-2008 binary32 value.
If value is an IEEE 754-2008 binary32 NaN value, return the NaN Number value.
Return the Number value that corresponds to value.
*/
var sign = (rawBytes[3] & 0x80) >> 7; // first bit
var exponent = ((rawBytes[3] & 0x7F) << 1) // 7 bits from index 3
| ((rawBytes[2] & 0x80) >> 7); // 1 bit from index 2
var mantissa = ((rawBytes[2] & 0x7F) << 16) // 7 bits from index 2
| (rawBytes[1] << 8) // 8 bits from index 1
| rawBytes[0]; // 8 bits from index 0
if (exponent === 0 && mantissa === 0) {
return sign === 0 ? 0 : -0;
}
if (exponent === 0xFF && mantissa === 0) {
return sign === 0 ? Infinity : -Infinity;
}
if (exponent === 0xFF && mantissa !== 0) {
return NaN;
}
exponent -= 127; // subtract the bias
// return $pow(-1, sign) * mantissa / $pow(2, 23) * $pow(2, exponent);
// return $pow(-1, sign) * (mantissa + 0x1000000) * $pow(2, exponent - 23);
return $pow(-1, sign) * (1 + (mantissa / $pow(2, 23))) * $pow(2, exponent);
}
if (type === 'Float64') { // step 4
/*
Let value be the byte elements of rawBytes concatenated and interpreted as a little-endian bit string encoding of an IEEE 754-2008 binary64 value.
If value is an IEEE 754-2008 binary64 NaN value, return the NaN Number value.
Return the Number value that corresponds to value.
*/
var sign = rawBytes[7] & 0x80 ? -1 : 1; // first bit
var exponent = ((rawBytes[7] & 0x7F) << 4) // 7 bits from index 7
| ((rawBytes[6] & 0xF0) >> 4); // 4 bits from index 6
var mantissa = ((rawBytes[6] & 0x0F) * 0x1000000000000) // 4 bits from index 6
+ (rawBytes[5] * 0x10000000000) // 8 bits from index 5
+ (rawBytes[4] * 0x100000000) // 8 bits from index 4
+ (rawBytes[3] * 0x1000000) // 8 bits from index 3
+ (rawBytes[2] * 0x10000) // 8 bits from index 2
+ (rawBytes[1] * 0x100) // 8 bits from index 1
+ rawBytes[0]; // 8 bits from index 0
if (exponent === 0 && mantissa === 0) {
return sign * 0;
}
if (exponent === 0x7FF && mantissa !== 0) {
return NaN;
}
if (exponent === 0x7FF && mantissa === 0) {
return sign * Infinity;
}
exponent -= 1023; // subtract the bias
return sign * (mantissa + 0x10000000000000) * $pow(2, exponent - 52);
}
// this is common to both branches
var intValue = 0;
for (var i = 0; i < rawBytes.length; i++) {
intValue |= rawBytes[i] << (8 * i);
}
/*
Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of an unsigned little-endian binary number.
*/
if ($charAt(type, 0) !== 'U') { // steps 5-6
// Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of a binary little-endian 2's complement number of bit length elementSize × 8.
var bitLength = elementSize * 8;
if (bitLength < 32) {
intValue = (intValue << (32 - bitLength)) >> (32 - bitLength);
}
}
return intValue; // step 7
};