[d565449] | 1 | 'use strict';
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| 2 |
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| 3 | var GetIntrinsic = require('get-intrinsic');
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| 4 |
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| 5 | var $pow = GetIntrinsic('%Math.pow%');
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| 6 |
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| 7 | module.exports = function bytesAsFloat64(rawBytes) {
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| 8 | // return new $Float64Array(new $Uint8Array(rawBytes).buffer)[0];
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| 9 |
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| 10 | /*
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| 11 | 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.
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| 12 | If value is an IEEE 754-2008 binary64 NaN value, return the NaN Number value.
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| 13 | Return the Number value that corresponds to value.
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| 14 | */
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| 15 | var sign = rawBytes[7] & 0x80 ? -1 : 1; // first bit
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| 16 | var exponent = ((rawBytes[7] & 0x7F) << 4) // 7 bits from index 7
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| 17 | | ((rawBytes[6] & 0xF0) >> 4); // 4 bits from index 6
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| 18 | var mantissa = ((rawBytes[6] & 0x0F) * 0x1000000000000) // 4 bits from index 6
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| 19 | + (rawBytes[5] * 0x10000000000) // 8 bits from index 5
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| 20 | + (rawBytes[4] * 0x100000000) // 8 bits from index 4
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| 21 | + (rawBytes[3] * 0x1000000) // 8 bits from index 3
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| 22 | + (rawBytes[2] * 0x10000) // 8 bits from index 2
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| 23 | + (rawBytes[1] * 0x100) // 8 bits from index 1
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| 24 | + rawBytes[0]; // 8 bits from index 0
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| 25 |
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| 26 | if (exponent === 0 && mantissa === 0) {
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| 27 | return sign * 0;
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| 28 | }
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| 29 | if (exponent === 0x7FF && mantissa !== 0) {
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| 30 | return NaN;
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| 31 | }
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| 32 | if (exponent === 0x7FF && mantissa === 0) {
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| 33 | return sign * Infinity;
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| 34 | }
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| 35 |
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| 36 | exponent -= 1023; // subtract the bias
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| 37 |
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| 38 | // Handle subnormal numbers
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| 39 | if (exponent === -1023) {
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| 40 | return sign * mantissa * 5e-324; // $pow(2, -1022 - 52)
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| 41 | }
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| 42 |
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| 43 | return sign * (1 + (mantissa / 0x10000000000000)) * $pow(2, exponent);
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| 44 | };
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