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35 lines
995 B
CoffeeScript
35 lines
995 B
CoffeeScript
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# If we ever need a seedable PRNG, we can use this.
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# http://coffeescriptcookbook.com/chapters/math/generating-predictable-random-numbers
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class Rand
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@className: "Rand"
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# if created without a seed, uses current time as seed
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constructor: (@seed) ->
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# Knuth and Lewis' improvements to Park and Miller's LCPRNG
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@multiplier = 1664525
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@modulo = 4294967296 # 2**32-1
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@offset = 1013904223
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unless @seed? and 0 <= seed < @modulo
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@seed = (new Date().valueOf() * new Date().getMilliseconds()) % @modulo
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# sets new seed value
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seed: (seed) ->
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@seed = seed
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# return a random integer 0 <= n < @modulo
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randn: =>
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# new_seed = (a * seed + c) % m
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@seed = (@multiplier * @seed + @offset) % @modulo
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# return a random float 0 <= f < 1.0
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randf: =>
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@randn() / @modulo
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# return a random int 0 <= f < n
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rand: (n) =>
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Math.floor @randf() * n
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# return a random int min <= f < max
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rand2: (min, max) =>
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min + @rand max - min
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module.exports = Rand
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