diff --git a/doc/lib.txt b/doc/lib.txt index e24db97e04..24ba0243e3 100644 --- a/doc/lib.txt +++ b/doc/lib.txt @@ -202,6 +202,9 @@ Math libraries * `mersenne `_ Mersenne twister random number generator. +* `random `_ + Fast and tiny random number generator. + * `stats `_ Statistical analysis diff --git a/lib/pure/random.nim b/lib/pure/random.nim new file mode 100644 index 0000000000..5a4d45c380 --- /dev/null +++ b/lib/pure/random.nim @@ -0,0 +1,86 @@ +# +# +# Nim's Runtime Library +# (c) Copyright 2016 Andreas Rumpf +# +# See the file "copying.txt", included in this +# distribution, for details about the copyright. +# + +## | Nim's standard random number generator. Based on +## | http://xoroshiro.di.unimi.it/ +## | http://xoroshiro.di.unimi.it/xoroshiro128plus.c + +include "system/inclrtl" +{.push debugger:off .} # the user does not want to trace a part + # of the standard library! + +# XXX Expose RandomGenState +type + RandomGenState = object + a0, a1: uint64 + +# racy for multi-threading but good enough for now: +var state = RandomGenState( + a0: 0x69B4C98CB8530805u64, + a1: 0xFED1DD3004688D67CAu64) # global for backwards compatibility + +proc rotl(x: uint64, k: uint64): uint64 = + result = (x shl k) or (x shr (64u64 - k)) + +proc next(s: var RandomGenState): uint64 = + let s0 = s.a0 + var s1 = s.a1 + result = s0 + s1 + s1 = s1 xor s0 + s.a0 = rotl(s0, 55) xor s1 xor (s1 shl 14) # a, b + s.a1 = rotl(s1, 36) # c + +proc skipRandomNumbers(s: var RandomGenState) = + ## This is the jump function for the generator. It is equivalent + ## to 2^64 calls to next(); it can be used to generate 2^64 + ## non-overlapping subsequences for parallel computations. + const helper = [0xbeac0467eba5facbu64, 0xd86b048b86aa9922u64] + var + s0 = 0u64 + s1 = 0u64 + for i in 0..high(helper): + for b in 0..< 64: + if (helper[i] and (1u64 shl uint64(b))) != 0: + s0 = s0 xor s.a0 + s1 = s1 xor s.a1 + discard next(s) + s.a0 = s0 + s.a1 = s1 + +proc random*(max: int): int {.benign.} = + ## Returns a random number in the range 0..max-1. The sequence of + ## random number is always the same, unless `randomize` is called + ## which initializes the random number generator with a "random" + ## number, i.e. a tickcount. + result = int(next(state) mod uint64(max)) + +proc random*(max: float): float {.benign.} = + ## Returns a random number in the range 0..