You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
42 lines
1.5 KiB
42 lines
1.5 KiB
'use strict'; |
|
|
|
var $pow = require('math-intrinsics/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); |
|
};
|
|
|