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hackergrrl/bisecting-numbers: :scissors: Integer-like number system where any number can be bisected to form infinite integer subsystems.

Integer-like number system where any number can be bisected to form infinite integer subsystems.

If used without bisection, bisecting numbers cover the integers (..., -3, -2, -1, 0, 1, 2, 3, ...) 1:1. They are represented in code as though as string, not number. This is to represent values larger than what number can provide, amongst other reasons (see nice properties below).

'50' is a valid bisecting number.

However, its superpower is that it can be bisected into an integer subsystem:

Once a number is bisected, it can be incremented and decremented only within its subsystem:

inc('50.0') => '50.1'

dec('50.0') => '50.-1'   // *not* 49

Bisection can also be nested:

bisect(bisect('50.1')) => '50.1.0.0'

inc('50.1.0.9') => '50.1.0.10'

Finally, any two bisecting numbers can also be compared. This is important. The absolute ordering of bisecting numbers is such that any bisection space fits entirely between the two integers in the upper space around it:

compare('50', '50.0') => -1  // 50.0 is larger than 50
compare('50.0', '51') => -1  // 50.0 is smaller than 51

// The entire infinite system 50.* fits between 50 and 51
compare('50', '50.19.53.14009') => -1
compare('50.19.53.14009', '51') => -1

It's true! 1 can be "bisected" to 1.1, which has an infinite number of values betweeen 1 and 2.

You could also bisect further by making it so bisect(1.1) => 1.01, and then increment in amounts of 0.01.

How do you decrement though? You can't make the a subsystem negative without negating the entire value!

Well, you could make it so bisect(1) => 1.5. Now values < 1.5 are "negative". You can increment such that inc(1.9) => 1.51, etc. You can decrement the same way, so that dec(1.5) => 1.4, and dec(1.1) => 1.54.

You could keep on applying awkward rules like this to achieve the same effect.

The real motivation for this module came from a desire for the following properties, for bisecting-between, that real numbers don't grant:

1. more infinite & less lossy than JS number
2. able to use a custom alphabet (01, 0123456789, 0123456789ABCDEF, etc) to maximize use of the printable character space
3. fairly easy for humans to read and gauge the ordering of number pairs
4. minimize the growth of the string length when increment and decrement are used, in favour of bisecting being more space expensive

var BisectingNumbers = require('bisecting-numbers')

$ node

> var bn = require('bisecting-numbers')('ABCDEFGHIJKLMNOPQRSTUVWXYZ')
undefined

> bn.zero()
'A'

> bn.inc('BBBB')
'BBBC'

> bn.dec('A')
'-B'

> bn.inc('ZZZ')
'BAAA'

> bn.bisect('FWE')
'FWE.A'

> bn.dec(bn.bisect('FWE')))
'FWE.-B'

> bn.compare('GO', 'GC')
1

> bn.compare('AB.FWEU', 'AB')
1

> bn.compare('AB', 'AB.-A')
-1

Returns an object that codifies the bisecting number system over the given string alphabet (where alphabet.charAt(0) is the zero value, the next is 1, etc). If not provided, the alphabet is the string '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.

Returns the alphabet's zero value as a bisecting number. 0 by default.

Increments num by one in its bisection space.

Decrements num by one in its bisection space.

Bisects num into its own new bisection space.

bn.bisect('41') => '41.0'

Comparison method, suitable for use in e.g. sort(). Returns -1 if a < b, 0 if a === b, and 1 if a > b.

bn.compare('41.9.-6', '41.8.-6') => 1

With npm installed, run

$ npm install bisecting-numbers

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