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 */

/* 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
}

/* 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;
}

/* 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(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. */
}

/* 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: 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*/