| 1 | 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.
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| 2 |
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| 3 | Int64 instances look and feel much like JS-native Numbers. By way of example ...
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| 4 | ```js
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| 5 | // First, let's illustrate the problem ...
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| 6 | > (0x123456789).toString(16)
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| 7 | '123456789' // <- what we expect.
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| 8 | > (0x123456789abcdef0).toString(16)
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| 9 | '123456789abcdf00' // <- Ugh! JS doesn't do big ints. :(
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| 10 |
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| 11 | // So let's create a couple Int64s using the above values ...
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| 12 |
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| 13 | // Require, of course
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| 14 | > Int64 = require('node-int64')
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| 15 |
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| 16 | // x's value is what we expect (the decimal value of 0x123456789)
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| 17 | > x = new Int64(0x123456789)
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| 18 | [Int64 value:4886718345 octets:00 00 00 01 23 45 67 89]
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| 19 |
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| 20 | // y's value is Infinity because it's outside the range of integer
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| 21 | // precision. But that's okay - it's still useful because it's internal
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| 22 | // representation (octets) is what we passed in
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| 23 | > y = new Int64('123456789abcdef0')
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| 24 | [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
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| 25 |
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| 26 | // Let's do some math. Int64's behave like Numbers. (Sorry, Int64 isn't
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| 27 | // for doing 64-bit integer arithmetic (yet) - it's just for carrying
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| 28 | // around int64 values
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| 29 | > x + 1
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| 30 | 4886718346
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| 31 | > y + 1
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| 32 | Infinity
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| 33 |
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| 34 | // Int64 string operations ...
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| 35 | > 'value: ' + x
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| 36 | 'value: 4886718345'
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| 37 | > 'value: ' + y
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| 38 | 'value: Infinity'
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| 39 | > x.toString(2)
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| 40 | '100100011010001010110011110001001'
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| 41 | > y.toString(2)
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| 42 | 'Infinity'
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| 43 |
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| 44 | // Use JS's isFinite() method to see if the Int64 value is in the
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| 45 | // integer-precise range of JS values
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| 46 | > isFinite(x)
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| 47 | true
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| 48 | > isFinite(y)
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| 49 | false
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| 50 |
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| 51 | // Get an octet string representation. (Yay, y is what we put in!)
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| 52 | > x.toOctetString()
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| 53 | '0000000123456789'
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| 54 | > y.toOctetString()
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| 55 | '123456789abcdef0'
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| 56 |
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| 57 | // Finally, some other ways to create Int64s ...
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| 58 |
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| 59 | // Pass hi/lo words
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| 60 | > new Int64(0x12345678, 0x9abcdef0)
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| 61 | [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
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| 62 |
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| 63 | // Pass a Buffer
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| 64 | > new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0]))
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| 65 | [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
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| 66 |
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| 67 | // Pass a Buffer and offset
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| 68 | > new Int64(new Buffer([0,0,0,0,0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0]), 4)
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| 69 | [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
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| 70 |
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| 71 | // Pull out into a buffer
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| 72 | > new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0])).toBuffer()
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| 73 | <Buffer 12 34 56 78 9a bc de f0>
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| 74 |
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| 75 | // Or copy into an existing one (at an offset)
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| 76 | > var buf = new Buffer(1024);
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| 77 | > new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0])).copy(buf, 512);
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| 78 | ```
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