For what it's worth, an article by Ben Pfaff titled "RFC: clc-compliant pseudo-random number generator" showed up today on Usenet's comp.lang.c newsgroup. I have pasted it in its entirety below.

One issue that comes up fairly often around here is the poor
quality of the pseudo-random number generators supplied with many
C implementations.  As a result, we have to recommend things like
using the high-order bits returned by rand() instead of the
low-order bits, avoiding using rand() for anything that wants
decently random numbers, not using rand() if you want more than
approx. UINT_MAX total different sequences, and so on.

So I wrote some PRNG code that uses RC4, with a seed of up to 256
bytes.  Here it is.  I believe it is clc-compliant.  Comments on
this and anything else are welcome.

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/*
 * prng.c - Portable, ISO C90 and C99 compliant high-quality
 * pseudo-random number generator based on the alleged RC4
 * cipher.  This PRNG should be suitable for most general-purpose
 * uses.  Not recommended for cryptographic or financial
 * purposes.  Not thread-safe.
 */

/*
 * Copyright (c) 2004 Ben Pfaff <[email protected]>.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the
 * following conditions are met:
 *
 * 1. Redistributions of source code must retain the above
 * copyright notice, this list of conditions and the following
 * disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following
 * disclaimer in the documentation and/or other materials
 * provided with the distribution.
 *
 * 3. The author's and contributors' names may not be used to
 * endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS
 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT
 * SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
 * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 * 
 */

#include "prng.h"
#include <assert.h>
#include <float.h>
#include <limits.h>
#include <math.h>
#include <time.h>

/* RC4-based pseudo-random state. */
static unsigned char s[256];
static int s_i, s_j;

/* Nonzero if PRNG has been seeded. */
static int seeded;

/* Take advantage of inlining if possible. */
#if __STDC_VERSION__ >= 199901L
#define INLINE inline
#else
#define INLINE
#endif

/* Swap bytes. */
static INLINE void
swap_byte (unsigned char *a, unsigned char *b) 
{
  unsigned char t = *a;
  *a = *b;
  *b = t;
}

/* If KEY is non-null and SIZE is nonzero, seeds the
   pseudo-random number generator based on the SIZE bytes in BUF.
   At most the first 256 bytes of BUF are used.  If KEY is a null
   pointer and SIZE is zero, seeds the pseudo-random number
   generator based on the current time.  

   If this function is not called by the user before any prng_get
   function, it is called automatically to obtain a time-based
   seed. */
void
prng_seed (const void *key_, size_t size) 
{
  const unsigned char *key = key_;
  size_t key_idx;
  int i, j;

  assert ((key != NULL && size > 0) || (key == NULL && size == 0));

  if (key == NULL) 
    {
      static time_t t;

      t = (t == 0) ? time (NULL) : t + 1;
      key = (void *) &t;
      size = sizeof t;
    }

  for (i = 0; i < 256; i++) 
    s[i] = i;
  for (key_idx = 0, i = j = 0; i < 256; i++) 
    {
      j = (j + s[i] + key[key_idx]) & 255;
      swap_byte (s + i, s + j);
      if (++key_idx >= size)
        key_idx = 0;
    }

  s_i = s_j = 0;
  seeded = 1;
}

/* Returns a pseudo-random integer in the range [0,255]. */
unsigned char
prng_get_octet (void)
{
  if (!seeded) 
    prng_seed (NULL, 0);

  s_i = (s_i + 1) & 255;
  s_j = (s_j + s[s_i]) & 255;
  swap_byte (s + s_i, s + s_j);

  return s[(s[s_i] + s[s_j]) & 255];
}

/* Returns a pseudo-random integer in the range [0,UCHAR_MAX]. */
unsigned char
prng_get_byte (void) 
{
  if (UCHAR_MAX == 255) 
    {
      /* Normal case for 8-bit bytes. */
      return prng_get_octet (); 
    }
  else 
    {
      /* Handle oversize bytes. */
      unsigned byte = prng_get_octet ();
      unsigned done = 255;
      while ((unsigned char) done != UCHAR_MAX) 
        {
          byte = (byte << 8) | prng_get_octet ();
          done = (done << 8) | 255;
        }
      return byte;
    }
}

/* Fills BUF with SIZE pseudo-random bytes. */
void
prng_get_bytes (void *buf_, size_t size) 
{
  unsigned char *buf;

  for (buf = buf_; size-- > 0; buf++)
    *buf = prng_get_byte (); 
}

/* Returns a pseudo-random unsigned long in the range [0,
   ULONG_MAX]. */
unsigned long
prng_get_ulong (void) 
{
  unsigned long ulng = prng_get_octet ();
  unsigned long done = 255;

  while (done != ULONG_MAX)
    {
      ulng = (ulng << 8) | prng_get_octet ();
      done = (done << 8) | 255;
    }

  return ulng;
}

/* Returns a pseudo-random long in the range [0, LONG_MAX]. */
long
prng_get_long (void) 
{
  for (;;)
    {
      unsigned ulng = prng_get_ulong ();
      if (ulng <= LONG_MAX)
        return ulng; 
    }
}

/* Returns a pseudo-random unsigned int in the range [0,
   UINT_MAX]. */
unsigned
prng_get_uint (void) 
{
  unsigned uint = prng_get_octet ();
  unsigned done = 255;

  while (done != UINT_MAX)
    {
      uint = (uint << 8) | prng_get_octet ();
      done = (done << 8) | 255;
    }

  return uint;
}

/* Returns a pseudo-random int in the range [0, INT_MAX]. */
int
prng_get_int (void) 
{
  for (;;)
    {
      unsigned uint = prng_get_uint ();
      if (uint <= INT_MAX)
        return uint; 
    }
}

/* Returns a pseudo-random floating-point number from the uniform
   distribution with range [0,1). */
double
prng_get_double (void) 
{
  for (;;) 
    {
      unsigned long ulng = prng_get_ulong ();
      if (ulng != ULONG_MAX)
        return (double) ulng / ULONG_MAX; 
    }
}

/* Returns a pseudo-random floating-point number from the
   distribution with mean 0 and standard deviation 1.  (Multiply
   the result by the desired standard deviation, then add the
   desired mean.) */
double 
prng_get_double_normal (void)
{
  /* Knuth, _The Art of Computer Programming_, Vol. 2, 3.4.1C,
     Algorithm P. */
  static double next_normal = DBL_MAX;
  double this_normal;
  
  if (next_normal != DBL_MAX)
    {
      this_normal = next_normal;
      next_normal = DBL_MAX;
    }
  else 
    {
      double v1, v2, s;
      
      do
        {
          double u1 = prng_get_double ();
          double u2 = prng_get_double ();
          v1 = 2.0 * u1 - 1.0;
          v2 = 2.0 * u2 - 1.0;
          s = v1 * v1 + v2 * v2;
        }
      while (s >= 1);

      this_normal = v1 * sqrt (-2. * log (s) / s);
      next_normal = v2 * sqrt (-2. * log (s) / s); 
    }
  
  return this_normal;
}
----------------------------------------------------------------------
#ifndef PRNG_H_INCLUDED
#define PRNG_H_INCLUDED

#include <stddef.h>

void prng_seed (const void *, size_t);
unsigned char prng_get_octet (void);
unsigned char prng_get_byte (void);
void prng_get_bytes (void *, size_t);
unsigned long prng_get_ulong (void);
long prng_get_long (void);
unsigned prng_get_uint (void);
int prng_get_int (void);
double prng_get_double (void);
double prng_get_double_normal (void);

#endif /* prng.h */
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-- 
"There's only one thing that will make them stop hating you.
 And that's being so good at what you do that they can't ignore you.
 I told them you were the best.  Now you damn well better be."
--Orson Scott Card, _Ender's Game_