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Annotation of imach/src/random.alw, revision 1.1

1.1     ! brouard     1: COMMENT:       RANDOM NUMBER GENERATOR
        !             2:                 ***********************
        !             3: 
        !             4:   PROCEDURE RANDOM RETURNS A LONG REAL RANDOM NUMBER UNIFORMLY
        !             5:       DISTRIBUTED IN (0,1) (INCLUDING 0 BUT NOT 1),
        !             6:       RANINIT(R) WITH R ANY INTEGER MUST BE CALLED FOR
        !             7:       INITIALIZATION BEFORE THE FIRST CALL TO RANDOM, AND THE
        !             8:       DECLARATIONS OF RAN1, RAN2 AND RAN3 MUST BE GLOBAL,
        !             9:       THE ALGORITHM RETURNS X(N)/2**56, WHERE
        !            10:                    X(N) = X(N-1) + X(N-127) (MOO 2**56),
        !            11:       SINCE 1 + X + X**127 IS PRIMITIVE (MOD 2), THE PERIOD IS AT
        !            12:       LEAST 2**127 - 1 > 10**38, SEE KNUTH (1969), PP. 26, 34, 464,
        !            13:       X(N) IS STORED IN A LONG REAL WORD AS
        !            14:       RAN3 = X(N)/2**56 - 1/2, AND ALL FLOATING POINT ARITHMETIC
        !            15:       IS EXACT;
        !            16: 
        !            17:   LONG REAL PROCEDURE RANDOM(INTEGER VALUE NAUGHT);
        !            18:   BEGIN
        !            19:     LONG REAL RAN1; INTEGER RAN2; LONG REAL ARRAY RAN3 (0::126);
        !            20:     INTEGER R; LOGICAL INIT;
        !            21:     INIT := FALSE;
        !            22:     IF INIT THEN GO TO L3;
        !            23:     R := ABS(NAUGHT) REM 8190 + 1;
        !            24:     RAN2 := 127; WHILE RAN2 > 0 DO
        !            25:     BEGIN RAN2 := RAN2 - 1; RAN1 := -2L**55;
        !            26:       FOR I := 1 UNTIL 7 DO
        !            27:       BEGIN R := (1756*R) REM 8191;
        !            28:         RAN1 := (RAN1 + (R DIV 32) )*( 1/256) ;
        !            29:       END;
        !            30:       RAN3 (RAN2) := RAN1
        !            31:     END;
        !            32:     INIT := TRUE;
        !            33:   L3: RAN2 := IF RAN2 = 0 THEN 126 ELSE RAN2 - 1;
        !            34:     RAN1 := RAN1 + RAN3 (RAN2);
        !            35:     RAN3 (RAN2) := RAN1 := IF RAN1 < 0L THEN RAN1 + 0.5L
        !            36:                         ELSE RAN1 - 0.5L;
        !            37:     RAN1 + 0.5L
        !            38:   END RANDOM.