Annotation of /sml/branches/SMLNJ/src/smlnj-lib/Util/1347-fix

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Revision 26 - (view) (download)
Original Path: sml/trunk/src/smlnj-lib/Util/1347-fix

1 :	monnier	26	Here is the fix for bug 1047, consisting of a new signature and new
2 :			structure.
3 :
4 :			Emden
5 :			=============== rand-sig.sml =========================
6 :			(* rand-sig.sml
7 :			*
8 :			* COPYRIGHT (c) 1993 by AT&T Bell Laboratories. See COPYRIGHT file for details.
9 :			* COPYRIGHT (c) 1998 by AT&T Laboratories.
10 :			*
11 :			* Signature for a simple random number generator.
12 :			*
13 :			*)
14 :
15 :			signature RAND =
16 :			sig
17 :
18 :			type rand = Word31.word
19 :
20 :			val randMin : rand
21 :			val randMax : rand
22 :
23 :			val random : rand -> rand
24 :			(* Given seed, return value randMin <= v <= randMax
25 :			* Iteratively using the value returned by random as the
26 :			* next seed to random will produce a sequence of pseudo-random
27 :			* numbers.
28 :			*)
29 :
30 :			val mkRandom : rand -> unit -> rand
31 :			(* Given seed, return function generating a sequence of
32 :			* random numbers randMin <= v <= randMax
33 :			*)
34 :
35 :			val norm : rand -> real
36 :			(* Map values in the range [randMin,randMax] to (0.0,1.0) *)
37 :
38 :			val range : (int * int) -> rand -> int
39 :			(* Map v, randMin <= v <= randMax, to integer range [i,j]
40 :			* Exception -
41 :			* Fail if j < i
42 :			*)
43 :
44 :			end (* RAND *)
45 :
46 :			============== rand.sml =====================
47 :			(* rand.sml
48 :			*
49 :			* COPYRIGHT (c) 1991 by AT&T Bell Laboratories. See COPYRIGHT file for details
50 :			* COPYRIGHT (c) 1998 by AT&T Laboratories. See COPYRIGHT file for details
51 :			*
52 :			* Random number generator taken from Paulson, pp. 170-171.
53 :			* Recommended by Stephen K. Park and Keith W. Miller,
54 :			* Random number generators: good ones are hard to find,
55 :			* CACM 31 (1988), 1192-1201
56 :			* Updated to include the new preferred multiplier of 48271
57 :			* CACM 36 (1993), 105-110
58 :			* Updated to use on Word31.
59 :			*
60 :			* Note: The Random structure provides a better generator.
61 :			*)
62 :
63 :			structure Rand : RAND =
64 :			struct
65 :
66 :			type rand = Word31.word
67 :			type rand' = Int32.int (* internal representation *)
68 :
69 :			val a : rand' = 48271
70 :			val m : rand' = 2147483647 (* 2^31 - 1 *)
71 :			val m_1 = m - 1
72 :			val q = m div a
73 :			val r = m mod a
74 :
75 :			val extToInt = Int32.fromLarge o Word31.toLargeInt
76 :			val intToExt = Word31.fromLargeInt o Int32.toLarge
77 :
78 :			val randMin : rand = 0w1
79 :			val randMax : rand = intToExt m_1
80 :
81 :			fun chk 0w0 = 1
82 :			| chk 0wx7fffffff = m_1
83 :			| chk seed = extToInt seed
84 :
85 :			fun random' seed = let
86 :			val hi = seed div q
87 :			val lo = seed mod q
88 :			val test = a * lo - r * hi
89 :			in
90 :			if test > 0 then test else test + m
91 :			end
92 :
93 :			val random = intToExt o random' o chk
94 :
95 :			fun mkRandom seed = let
96 :			val seed = ref (chk seed)
97 :			in
98 :			fn () => (seed := random' (!seed); intToExt (!seed))
99 :			end
100 :
101 :			val real_m = Real.fromLargeInt (Int32.toLarge m)
102 :			fun norm s = (Real.fromLargeInt (Word31.toLargeInt s)) / real_m
103 :
104 :			fun range (i,j) =
105 :			if j < i
106 :			then LibBase.failure{module="Random",func="range",msg="hi < lo"}
107 :			else if j = i then fn _ => i
108 :			else let
109 :			val R = Int32.fromInt j - Int32.fromInt i
110 :			val cvt = Word31.toIntX o Word31.fromLargeInt o Int32.toLarge
111 :			in
112 :			if R = m then Word31.toIntX
113 :			else fn s => i + cvt ((extToInt s) mod (R+1))
114 :			end
115 :
116 :			end (* Rand *)
117 :
118 :
119 :

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