Nim implementation of the standard unix drand48 pseudo random number generator


Drand48 Build Status

Nim implementation of the standard unix drand48 pseudo random number generator.

All the routines work by generating a sequence of 48-bit integer values, Xi , according to the linear congruential formula:

Xn+1 = (aXn + c) mod m n>= 0

The parameter m = 248; hence 48-bit integer arithmetic is performed. The multiplier value a and the addend value c are given by:

a = 0x5DEECE66D = 0c273673163155 c = 0xB = oc13

The value returned by any of the drand48() is computed by first generating the next 48-bit Xi in the sequence. Then the appropriate number of bits, according to the type of data item to be returned, are copied from the high-order (leftmost) bits of Xi and transformed into the returned value.

The drand48() function stores the last 48-bit Xi generated in an internal buffer; that is why they must be initialised prior to being invoked.

The initializer function srand48() sets the high-order 32 bits of Xi to the low-order 32 bits contained in its argument. The low-order 16 bits of Xi are set to the arbitrary value 0x330E .

The initializer function seed48() sets the value of Xi to the 48-bit value specified in the argument array. The seed can be set with the 48-bit seed split into four 12-bit chunks, or as a 48-bit int.

There are functions savern12() and savern48() that returns the current random number seed.

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License: BSD 3-Clause

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