You've already forked setup-python
mirror of
https://github.com/actions/setup-python.git
synced 2025-10-31 07:06:25 +07:00
79 lines
2.6 KiB
Markdown
79 lines
2.6 KiB
Markdown
JavaScript Numbers are represented as [IEEE 754 double-precision floats](http://steve.hollasch.net/cgindex/coding/ieeefloat.html). Unfortunately, this means they lose integer precision for values beyond +/- 2^^53. For projects that need to accurately handle 64-bit ints, such as [node-thrift](https://github.com/wadey/node-thrift), a performant, Number-like class is needed. Int64 is that class.
|
|
|
|
Int64 instances look and feel much like JS-native Numbers. By way of example ...
|
|
```js
|
|
// First, let's illustrate the problem ...
|
|
> (0x123456789).toString(16)
|
|
'123456789' // <- what we expect.
|
|
> (0x123456789abcdef0).toString(16)
|
|
'123456789abcdf00' // <- Ugh! JS doesn't do big ints. :(
|
|
|
|
// So let's create a couple Int64s using the above values ...
|
|
|
|
// Require, of course
|
|
> Int64 = require('node-int64')
|
|
|
|
// x's value is what we expect (the decimal value of 0x123456789)
|
|
> x = new Int64(0x123456789)
|
|
[Int64 value:4886718345 octets:00 00 00 01 23 45 67 89]
|
|
|
|
// y's value is Infinity because it's outside the range of integer
|
|
// precision. But that's okay - it's still useful because it's internal
|
|
// representation (octets) is what we passed in
|
|
> y = new Int64('123456789abcdef0')
|
|
[Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
|
|
|
|
// Let's do some math. Int64's behave like Numbers. (Sorry, Int64 isn't
|
|
// for doing 64-bit integer arithmetic (yet) - it's just for carrying
|
|
// around int64 values
|
|
> x + 1
|
|
4886718346
|
|
> y + 1
|
|
Infinity
|
|
|
|
// Int64 string operations ...
|
|
> 'value: ' + x
|
|
'value: 4886718345'
|
|
> 'value: ' + y
|
|
'value: Infinity'
|
|
> x.toString(2)
|
|
'100100011010001010110011110001001'
|
|
> y.toString(2)
|
|
'Infinity'
|
|
|
|
// Use JS's isFinite() method to see if the Int64 value is in the
|
|
// integer-precise range of JS values
|
|
> isFinite(x)
|
|
true
|
|
> isFinite(y)
|
|
false
|
|
|
|
// Get an octet string representation. (Yay, y is what we put in!)
|
|
> x.toOctetString()
|
|
'0000000123456789'
|
|
> y.toOctetString()
|
|
'123456789abcdef0'
|
|
|
|
// Finally, some other ways to create Int64s ...
|
|
|
|
// Pass hi/lo words
|
|
> new Int64(0x12345678, 0x9abcdef0)
|
|
[Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
|
|
|
|
// Pass a Buffer
|
|
> new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0]))
|
|
[Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
|
|
|
|
// Pass a Buffer and offset
|
|
> new Int64(new Buffer([0,0,0,0,0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0]), 4)
|
|
[Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
|
|
|
|
// Pull out into a buffer
|
|
> new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0])).toBuffer()
|
|
<Buffer 12 34 56 78 9a bc de f0>
|
|
|
|
// Or copy into an existing one (at an offset)
|
|
> var buf = new Buffer(1024);
|
|
> new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0])).copy(buf, 512);
|
|
```
|