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(* rand.sml * * COPYRIGHT (c) 1991 by AT&T Bell Laboratories. See COPYRIGHT file for details * * Random number generator taken from Paulson, pp. 170-171. * Recommended by Stephen K. Park and Keith W. Miller, * Random number generators: good ones are hard to find, * CACM 31 (1988), 1192-1201 * Updated to include the new preferred multiplier of 48271 * CACM 36 (1993), 105-110 * * Note: The Random structure provides a better generator. *) structure Rand : RAND = struct (* real number version for systems with 46-bit mantissas *) val a = 48271.0 and m = 2147483647.0 val randMin = 1.0 val randMax = m - 1.0 fun random seed = let val t = a*seed in t - m * real(floor(t/m)) end fun mkRandom seed = let val seed = ref seed in fn () => (seed := random (!seed); !seed) end fun norm r = r / m fun range (i,j) = if j < i then LibBase.failure{module="Random",func="range",msg="hi < lo"} else let val R = real(j - i + 1) in fn r => i + floor(R*(r/m)) end handle _ => let val ri = real i val R = (real j)-ri+1.0 in fn r => floor(ri + R*(r/m)) end end (* Rand *)

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