ProfitPress Mega CDROM2 …eeware (MSDOS)(1992)(Eng)/ProfitPress-MegaCDROM2.B6I/PROG/MISC/BD3.ZIP/RANDOM.LST

File List | 1989-03-12 | 4.0 KB | 102 lines

  1 package RANDOM is
  2 --------------------------------------------------------------------------
  3 --| BEGIN PROLOGUE
  4 --| DESCRIPTION            : Package RANDOM contains the function NUMBER
  5 --|                        : which returns a pseudo-random number
  6 --|                        : of type FLOAT in the range 0.0 .. 1.0.
  7 --|                        :
  8 --| REQUIREMENTS SUPPORTED : Random Number Generator
  9 --|                        :
 10 --| LIMITATIONS            : None
 11 --|                        :
 12 --| AUTHOR(S)              : Richard Conn (RLC) from Bill Whitaker's work
 13 --| CHANGE LOG             : 09/30/88  RLC  Design, code, test from
 14 --|                        :                 Bill Whitaker's original work
 15 --|                        : 10/11/88  RLC  Modified based on ideas from
 16 --|                        :                 Ron Bell and his RAN2 Package
 17 --|                        :
 18 --| REMARKS                : None
 19 --|                        :
 20 --| PORTABILITY ISSUES     : Uses 16-bit integers, so should be quite
 21 --|                        : portable
 22 --| END PROLOGUE
 23 --------------------------------------------------------------------------
 24
 25     function NUMBER return FLOAT;
 26     -- Return a floating point pseudo-random number
 27
 28 end RANDOM;
 29 --
 30 with CALENDAR;
 31 package body RANDOM is
 32
 33     X : INTEGER;
 34     Y : INTEGER;
 35     Z : INTEGER;
 36
 37     --=============================================================
 38     function CONVERT_TO_FLOAT(ITEM : in INTEGER) return FLOAT is
 39     -- This function is necessary for some optimizing compilers
 40     -- in order to prevent expressions like FLOAT(INTEGER(FLOAT))
 41     -- from being optimized away
 42     begin
 43         return FLOAT(ITEM);
 44     end CONVERT_TO_FLOAT;
 45
 46     --=============================================================
 47     procedure SEED is
 48     -- Generate seed values for X, Y, and Z using Package CALENDAR
 49         DAY_MONTH : FLOAT;
 50         SECONDS   : FLOAT;
 51         HUNDREDS  : FLOAT;
 52
 53     begin
 54         SECONDS := FLOAT(CALENDAR.SECONDS(CALENDAR.CLOCK));
 55         HUNDREDS := (SECONDS/2.88) -
 56             CONVERT_TO_FLOAT(INTEGER((SECONDS/2.88) - 0.5));
 57         DAY_MONTH := FLOAT(CALENDAR.DAY(CALENDAR.CLOCK) *
 58             CALENDAR.MONTH(CALENDAR.CLOCK));
 59         X := INTEGER(SECONDS/2.88);
 60         Y := INTEGER(HUNDREDS * 30000.0);
 61         Z := INTEGER(DAY_MONTH/372.0 * SECONDS * 30000.0);
 62     end SEED;
 63
 64 --
 65 -- Package body RANDOM
 66
 67     --=============================================================
 68     function NUMBER return FLOAT is
 69     --  This rectangular random number routine is adapted from a report
 70     --  "A Pseudo-Random Number Generator" by B. A. Wichmann and I. D. Hill
 71     --  NPL Report DNACS XX (to be published)
 72     --  In this version, it is suitable for machines supporting
 73     --  INTEGER at only 16 bits and is portable in Ada
 74
 75         W : FLOAT;
 76
 77     begin
 78         X := 171 * (X mod 177) - 2 * (X / 177);
 79         -- Used to be: X := 171 * (X mod 177 - 177) - 2 * (X / 177);
 80         if X < 0 then
 81             X := X + 30269;
 82         end if;
 83         Y := 172 * (Y mod 176) - 35 * (Y / 176);
 84         if Y < 0 then
 85             Y := Y + 30307;
 86         end if;
 87         Z := 170 * (Z mod 178) - 63 * (Z / 178);
 88         if Z < 0 then
 89             Z := Z + 30323;
 90         end if;
 91
 92         W := FLOAT(X) / 30269.0 + FLOAT(Y) / 30307.0 + FLOAT(Z) / 30323.0;
 93         return W - CONVERT_TO_FLOAT(INTEGER(W - 0.5));
 94     end NUMBER;
 95
 96 --=============================================================
 97 begin
 98
 99     SEED; -- Initialize random number generator
100
101 end RANDOM;