Source:NetHack 3.6.0/src/rnd.c

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 /* NetHack 3.6	rnd.c	$NHDT-Date: 1446883921 2015/11/07 08:12:01 $  $NHDT-Branch: master $:$NHDT-Revision: 1.16 $ */
 /* NetHack may be freely redistributed.  See license for details. */
 
 #include "hack.h"
 
 /* "Rand()"s definition is determined by [OS]conf.h */
 #if defined(LINT) && defined(UNIX) /* rand() is long... */
 extern int NDECL(rand);
 #define RND(x) (rand() % x)
 #else /* LINT */
 #if defined(UNIX) || defined(RANDOM)
 #define RND(x) ((int) (Rand() % (long) (x)))
 #else
 /* Good luck: the bottom order bits are cyclic. */
 #define RND(x) ((int) ((Rand() >> 3) % (x)))
 #endif
 #endif /* LINT */
 

rn2

 /* 0 <= rn2(x) < x */
 int
 rn2(x)
 register int x;
 {
 #ifdef BETA
     if (x <= 0) {
         impossible("rn2(%d) attempted", x);
         return 0;
     }
     x = RND(x);
     return x;
 #else
     return RND(x);
 #endif
 }
 

rnl

 /* 0 <= rnl(x) < x; sometimes subtracting Luck;
    good luck approaches 0, bad luck approaches (x-1) */
 int
 rnl(x)
 register int x;
 {
     register int i, adjustment;
 
 #ifdef BETA
     if (x <= 0) {
         impossible("rnl(%d) attempted", x);
         return 0;
     }
 #endif
 
     adjustment = Luck;
     if (x <= 15) {
         /* for small ranges, use Luck/3 (rounded away from 0);
            also guard against architecture-specific differences
            of integer division involving negative values */
         adjustment = (abs(adjustment) + 1) / 3 * sgn(adjustment);
         /*
          *       11..13 ->  4
          *        8..10 ->  3
          *        5.. 7 ->  2
          *        2.. 4 ->  1
          *       -1,0,1 ->  0 (no adjustment)
          *       -4..-2 -> -1
          *       -7..-5 -> -2
          *      -10..-8 -> -3
          *      -13..-11-> -4
          */
     }
 
     i = RND(x);
     if (adjustment && rn2(37 + abs(adjustment))) {
         i -= adjustment;
         if (i < 0)
             i = 0;
         else if (i >= x)
             i = x - 1;
     }
     return i;
 }
 

rnd

 /* 1 <= rnd(x) <= x */
 int
 rnd(x)
 register int x;
 {
 #ifdef BETA
     if (x <= 0) {
         impossible("rnd(%d) attempted", x);
         return 1;
     }
 #endif
     x = RND(x) + 1;
     return x;
 }
 

d

 /* d(N,X) == NdX == dX+dX+...+dX N times; n <= d(n,x) <= (n*x) */
 int
 d(n, x)
 register int n, x;
 {
     register int tmp = n;
 
 #ifdef BETA
     if (x < 0 || n < 0 || (x == 0 && n != 0)) {
         impossible("d(%d,%d) attempted", n, x);
         return 1;
     }
 #endif
     while (n--)
         tmp += RND(x);
     return tmp; /* Alea iacta est. -- J.C. */
 }
 

rne

 /* 1 <= rne(x) <= max(u.ulevel/3,5) */
 int
 rne(x)
 register int x;
 {
     register int tmp, utmp;
 
     utmp = (u.ulevel < 15) ? 5 : u.ulevel / 3;
     tmp = 1;
     while (tmp < utmp && !rn2(x))
         tmp++;
     return tmp;
 
     /* was:
      *  tmp = 1;
      *  while (!rn2(x))
      *    tmp++;
      *  return min(tmp, (u.ulevel < 15) ? 5 : u.ulevel / 3);
      * which is clearer but less efficient and stands a vanishingly
      * small chance of overflowing tmp
      */
 }
 

rnz

 /* rnz: everyone's favorite! */
 int
 rnz(i)
 int i;
 {
 #ifdef LINT
     int x = i;
     int tmp = 1000;
 #else
     register long x = (long) i;
     register long tmp = 1000L;
 #endif
 
     tmp += rn2(1000);
     tmp *= rne(4);
     if (rn2(2)) {
         x *= tmp;
         x /= 1000;
     } else {
         x *= 1000;
         x /= tmp;
     }
     return (int) x;
 }
 
 /*rnd.c*/