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| 1 : | monnier | 26 | (* rand.sml |
| 2 : | * | ||
| 3 : | * COPYRIGHT (c) 1991 by AT&T Bell Laboratories. See COPYRIGHT file for details | ||
| 4 : | * | ||
| 5 : | * Random number generator taken from Paulson, pp. 170-171. | ||
| 6 : | * Recommended by Stephen K. Park and Keith W. Miller, | ||
| 7 : | * Random number generators: good ones are hard to find, | ||
| 8 : | * CACM 31 (1988), 1192-1201 | ||
| 9 : | * Updated to include the new preferred multiplier of 48271 | ||
| 10 : | * CACM 36 (1993), 105-110 | ||
| 11 : | * | ||
| 12 : | * Note: The Random structure provides a better generator. | ||
| 13 : | *) | ||
| 14 : | |||
| 15 : | structure Rand : RAND = | ||
| 16 : | struct | ||
| 17 : | |||
| 18 : | (* real number version for systems with 46-bit mantissas *) | ||
| 19 : | val a = 48271.0 and m = 2147483647.0 | ||
| 20 : | |||
| 21 : | val randMin = 1.0 | ||
| 22 : | val randMax = m - 1.0 | ||
| 23 : | |||
| 24 : | fun random seed = let | ||
| 25 : | val t = a*seed | ||
| 26 : | in | ||
| 27 : | t - m * real(floor(t/m)) | ||
| 28 : | end | ||
| 29 : | |||
| 30 : | fun mkRandom seed = let | ||
| 31 : | val seed = ref seed | ||
| 32 : | in | ||
| 33 : | fn () => (seed := random (!seed); !seed) | ||
| 34 : | end | ||
| 35 : | |||
| 36 : | fun norm r = r / m | ||
| 37 : | |||
| 38 : | fun range (i,j) = | ||
| 39 : | if j < i | ||
| 40 : | then LibBase.failure{module="Random",func="range",msg="hi < lo"} | ||
| 41 : | else let | ||
| 42 : | val R = real(j - i + 1) | ||
| 43 : | in | ||
| 44 : | fn r => i + floor(R*(r/m)) | ||
| 45 : | end handle _ => let | ||
| 46 : | val ri = real i | ||
| 47 : | val R = (real j)-ri+1.0 | ||
| 48 : | in | ||
| 49 : | fn r => floor(ri + R*(r/m)) | ||
| 50 : | end | ||
| 51 : | |||
| 52 : | end (* Rand *) | ||
| 53 : |
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