<INTERFACE> The <CD/Random/ structure <SEEALSO> <STRREF TOPID/Rand/ </SEEALSO> <PP> The <STRREF NOLINK/Random/ structure implements a random number generator using a subtract-with-borrow (SWB) generator as described in Marsaglia and Zaman, "A New Class of Random Number Generators," <IT/Ann. Applied Prob./ 1(3), 1991, pp. 462-480. <PP> The SWB generator is a 31-bit generator with lags 48 and 8. It has period (2<SUP/1487/ - 2<SUP/247/)/105 or about <MATH/10<SUP/445//. Although generally excellent, they act locally like a lagged Fibonacci generator and thus have troubles with the birthday test. To repair this, the implementation provided here incorporates a suggestion of Marsaglia and Zaman, and combines the SWB generator with a linear congruential generator, specifically <MATH/(48271*a)mod(2<SUP/31/-1)/. <OPAQUE> <SPEC> <TYPE><ID>rand <COMMENT> <PP> encapsulates state for the random number generator. <SPEC> <VAL>rand<TY>(int * int) -> rand <COMMENT> <PROTOTY> rand (<ARG/i/, <ARG/j/) </PROTOTY> creates the initial seed for the random number generator based on the integers <ARG/i/ and <ARG/j/. <SPEC> <VAL>toString<TY>rand -> string <VAL>fromString<TY>string -> rand <COMMENT> <PP> These functions convert between generator state and a string representation of that state. The string representation is not necessarily printable. <CD/fromString/ is only guaranteed to work on the output of <CD/toString/, in which case <CD/fromString o toString/ is the identity function. A string in an incorrect format will cause <CD/fromString/ to raise the exception. <PP> These functions allow the state of a generator to be saved, in order that the generator can be replicated at a later time. <SPEC> <VAL>randInt<TY>rand -> int <COMMENT> <PROTOTY> randInt <ARG/s/ </PROTOTY> generates random integers uniformly in the range [Int.minInt, Int.maxInt] based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. <SPEC> <VAL>randNat<TY>rand -> int <COMMENT> <PROTOTY> randNat <ARG/s/ </PROTOTY> generates random integers uniformly in the range [0, Int.maxInt] based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. <SPEC> <VAL>randReal<TY>rand -> real <COMMENT> <PROTOTY> randReal <ARG/s/ </PROTOTY> generates random integers uniformly in the range <MATH/(0.0,1.0)/ based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. <SPEC> <VAL>randRange<TY>(int * int) -> rand -> int <RAISES> <PROTOTY> randRange (<ARG/i/, <ARG/j/) <ARG/s/ </PROTOTY> generates random integers uniformly in the range <MATH/[<ARG/i/, <ARG/j/]/ based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. This raises the exception </INTERFACE>