45 lines
1.5 KiB
JavaScript
45 lines
1.5 KiB
JavaScript
'use strict';
|
|
|
|
var GetIntrinsic = require('get-intrinsic');
|
|
|
|
var $pow = GetIntrinsic('%Math.pow%');
|
|
|
|
module.exports = function bytesAsFloat64(rawBytes) {
|
|
// return new Float64Array(new Uint8Array(rawBytes).buffer)[0];
|
|
|
|
/*
|
|
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
|
|
|
|
// Handle subnormal numbers
|
|
if (exponent === -1023) {
|
|
return sign * mantissa * 5e-324; // $pow(2, -1022 - 52)
|
|
}
|
|
|
|
return sign * (1 + (mantissa / 0x10000000000000)) * $pow(2, exponent);
|
|
};
|