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Cream of the Crop 1
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NRPAS13.ARJ
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RAN3.PAS
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Pascal/Delphi Source File
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1991-04-29
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2KB
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59 lines
FUNCTION ran3(VAR idum: integer): real;
(* Programs using RAN3 must declare the following variables
VAR
glinext,glinextp: integer;
glma: ARRAY [1..55] OF real;
in the main routine. Machines with 4-byte integers can use the integer
implementation of this routine, substituting glma of type integer, the
commented CONST and VAR declarations, and the MOD function in the third
line after the BEGIN. *)
(* CONST
mbig=1000000000;
mseed=161803398;
mz=0;
fac=1.0e-9;
VAR
i,ii,k,mj,mk: integer; *)
CONST
mbig=4.0e6;
mseed=1618033.0;
mz=0.0;
fac=2.5e-7; (* 1/mbig *)
VAR
i,ii,k: integer;
mj,mk: real;
BEGIN
IF (idum < 0) THEN BEGIN
mj := mseed+idum;
(* The following IF block is mj := mj MOD mbig; for real variables. *)
IF mj>=0.0 THEN mj := mj-mbig*trunc(mj/mbig)
ELSE mj := mbig-abs(mj)+mbig*trunc(abs(mj)/mbig);
glma[55] := mj;
mk := 1;
FOR i := 1 TO 54 DO BEGIN
ii := 21*i MOD 55;
glma[ii] := mk;
mk := mj-mk;
IF (mk < mz) THEN mk := mk+mbig;
mj := glma[ii]
END;
FOR k := 1 TO 4 DO BEGIN
FOR i := 1 TO 55 DO BEGIN
glma[i] := glma[i]-glma[1+((i+30) MOD 55)];
IF (glma[i] < mz) THEN glma[i] := glma[i]+mbig
END
END;
glinext := 0;
glinextp := 31;
idum := 1
END;
glinext := glinext+1;
IF (glinext = 56) THEN glinext := 1;
glinextp := glinextp+1;
IF (glinextp = 56) THEN glinextp := 1;
mj := glma[glinext]-glma[glinextp];
IF (mj < mz) THEN mj := mj+mbig;
glma[glinext] := mj;
ran3 := mj*fac
END;