/*
   +----------------------------------------------------------------------+
   | PHP HTML Embedded Scripting Language Version 3.0                     |
   +----------------------------------------------------------------------+
   | Copyright (c) 1997-2000 PHP Development Team (See Credits file)      |
   +----------------------------------------------------------------------+
   | This program is free software; you can redistribute it and/or modify |
   | it under the terms of one of the following licenses:                 |
   |                                                                      |
   |  A) the GNU General Public License as published by the Free Software |
   |     Foundation; either version 2 of the License, or (at your option) |
   |     any later version.                                               |
   |                                                                      |
   |  B) the PHP License as published by the PHP Development Team and     |
   |     included in the distribution in the file: LICENSE                |
   |                                                                      |
   | This program is distributed in the hope that it will be useful,      |
   | but WITHOUT ANY WARRANTY; without even the implied warranty of       |
   | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        |
   | GNU General Public License for more details.                         |
   |                                                                      |
   | You should have received a copy of both licenses referred to here.   |
   | If you did not, or have any questions about PHP licensing, please    |
   | contact core@php.net.                                                |
   +----------------------------------------------------------------------+
   | Authors: Rasmus Lerdorf <rasmus@lerdorf.on.ca>                       |
   |          Zeev Suraski <bourbon@netvision.net.il                      |
   |          Pedro Melo <melo@ip.pt>                                     |
   |                                                                      |
   | Based on code from: Shawn Cokus <Cokus@math.washington.edu>          |
   +----------------------------------------------------------------------+
 */
/* $Id: rand.c,v 1.39 2000/05/22 17:31:41 hholzgra Exp $ */

#include <stdlib.h>

#include "php.h"
#include "internal_functions.h"
#include "phpmath.h"

#ifndef RAND_MAX
#define RAND_MAX (1<<15)

#endif

/*
   This is the ``Mersenne Twister'' random number generator MT19937, which
   generates pseudorandom integers uniformly distributed in 0..(2^32 - 1)
   starting from any odd seed in 0..(2^32 - 1).  This version is a recode
   by Shawn Cokus (Cokus@math.washington.edu) on March 8, 1998 of a version by
   Takuji Nishimura (who had suggestions from Topher Cooper and Marc Rieffel in
   July-August 1997).
  
   Effectiveness of the recoding (on Goedel2.math.washington.edu, a DEC Alpha
   running OSF/1) using GCC -O3 as a compiler: before recoding: 51.6 sec. to
   generate 300 million random numbers; after recoding: 24.0 sec. for the same
   (i.e., 46.5% of original time), so speed is now about 12.5 million random
   number generations per second on this machine.
  
   According to the URL <http://www.math.keio.ac.jp/~matumoto/emt.html>
   (and paraphrasing a bit in places), the Mersenne Twister is ``designed
   with consideration of the flaws of various existing generators,'' has
   a period of 2^19937 - 1, gives a sequence that is 623-dimensionally
   equidistributed, and ``has passed many stringent tests, including the
   die-hard test of G. Marsaglia and the load test of P. Hellekalek and
   S. Wegenkittl.''  It is efficient in memory usage (typically using 2506
   to 5012 bytes of static data, depending on data type sizes, and the code
   is quite short as well).  It generates random numbers in batches of 624
   at a time, so the caching and pipelining of modern systems is exploited.
   It is also divide- and mod-free.
  
   This library is free software; you can redistribute it and/or modify it
   under the terms of the GNU Library General Public License as published by
   the Free Software Foundation (either version 2 of the License or, at your
   option, any later version).  This library is distributed in the hope that
   it will be useful, but WITHOUT ANY WARRANTY, without even the implied
   warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
   the GNU Library General Public License for more details.  You should have
   received a copy of the GNU Library General Public License along with this
   library; if not, write to the Free Software Foundation, Inc., 59 Temple
   Place, Suite 330, Boston, MA 02111-1307, USA.
  
   The code as Shawn received it included the following notice:
  
     Copyright (C) 1997 Makoto Matsumoto and Takuji Nishimura.  When
     you use this, send an e-mail to <matumoto@math.keio.ac.jp> with
     an appropriate reference to your work.
  
   It would be nice to CC: <Cokus@math.washington.edu> when you write.
  

  
   uint32 must be an unsigned integer type capable of holding at least 32
   bits; exactly 32 should be fastest, but 64 is better on an Alpha with
   GCC at -O3 optimization so try your options and see what's best for you
  
   Melo: we should put some ifdefs here to catch those alphas...
*/

typedef unsigned int uint32;

#define N             (624)                /* length of state vector */
#define M             (397)                /* a period parameter */
#define K             (0x9908B0DFU)        /* a magic constant */
#define hiBit(u)      ((u) & 0x80000000U)  /* mask all but highest   bit of u */
#define loBit(u)      ((u) & 0x00000001U)  /* mask all but lowest    bit of u */
#define loBits(u)     ((u) & 0x7FFFFFFFU)  /* mask     the highest   bit of u */
#define mixBits(u, v) (hiBit(u)|loBits(v)) /* move hi bit of u to hi bit of v */

#define MT_RAND_MAX 2147483647

static uint32   state[N+1];  /* state vector + 1 extra to not violate ANSI C */
static uint32   *next;       /* next random value is computed from here */
static int      left = -1;   /* can *next++ this many times before reloading */


static void seedMT(uint32 seed)
{
    /*
       We initialize state[0..(N-1)] via the generator
      
         x_new = (69069 * x_old) mod 2^32
      
       from Line 15 of Table 1, p. 106, Sec. 3.3.4 of Knuth's
       _The Art of Computer Programming_, Volume 2, 3rd ed.
      
       Notes (SJC): I do not know what the initial state requirements
       of the Mersenne Twister are, but it seems this seeding generator
       could be better.  It achieves the maximum period for its modulus
       (2^30) iff x_initial is odd (p. 20-21, Sec. 3.2.1.2, Knuth); if
       x_initial can be even, you have sequences like 0, 0, 0, ...;
       2^31, 2^31, 2^31, ...; 2^30, 2^30, 2^30, ...; 2^29, 2^29 + 2^31,
       2^29, 2^29 + 2^31, ..., etc. so I force seed to be odd below.
      
       Even if x_initial is odd, if x_initial is 1 mod 4 then
      
         the          lowest bit of x is always 1,
         the  next-to-lowest bit of x is always 0,
         the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
         the 3rd-from-lowest bit of x 4-cycles        ... 0 1 1 0 0 1 1 0 ... ,
         the 4th-from-lowest bit of x has the 8-cycle ... 0 0 0 1 1 1 1 0 ... ,
          ...
      
       and if x_initial is 3 mod 4 then
      
         the          lowest bit of x is always 1,
         the  next-to-lowest bit of x is always 1,
         the 2nd-from-lowest bit of x alternates      ... 0 1 0 1 0 1 0 1 ... ,
         the 3rd-from-lowest bit of x 4-cycles        ... 0 0 1 1 0 0 1 1 ... ,
         the 4th-from-lowest bit of x has the 8-cycle ... 0 0 1 1 1 1 0 0 ... ,
          ...
      
       The generator's potency (min. s>=0 with (69069-1)^s = 0 mod 2^32) is
       16, which seems to be alright by p. 25, Sec. 3.2.1.3 of Knuth.  It
       also does well in the dimension 2..5 spectral tests, but it could be
       better in dimension 6 (Line 15, Table 1, p. 106, Sec. 3.3.4, Knuth).
      
       Note that the random number user does not see the values generated
       here directly since reloadMT() will always munge them first, so maybe
       none of all of this matters.  In fact, the seed values made here could
       even be extra-special desirable if the Mersenne Twister theory says
       so-- that's why the only change I made is to restrict to odd seeds.
    */

    register uint32 x = (seed | 1U) & 0xFFFFFFFFU, *s = state;
    register int    j;

    for(left=0, *s++=x, j=N; --j;
        *s++ = (x*=69069U) & 0xFFFFFFFFU);
}


static uint32 reloadMT(void)
{
    register uint32 *p0=state, *p2=state+2, *pM=state+M, s0, s1;
    register int    j;

    if(left < -1)
        seedMT(4357U);

    left=N-1, next=state+1;

    for(s0=state[0], s1=state[1], j=N-M+1; --j; s0=s1, s1=*p2++)
        *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

    for(pM=state, j=M; --j; s0=s1, s1=*p2++)
        *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

    s1=state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
    s1 ^= (s1 >> 11);
    s1 ^= (s1 <<  7) & 0x9D2C5680U;
    s1 ^= (s1 << 15) & 0xEFC60000U;
    return(s1 ^ (s1 >> 18));
}


static inline uint32 randomMT(void)
{
    uint32 y;

    if(--left < 0)
        return(reloadMT());

    y  = *next++;
    y ^= (y >> 11);
    y ^= (y <<  7) & 0x9D2C5680U;
    y ^= (y << 15) & 0xEFC60000U;
    return(y ^ (y >> 18));
}


#if HAVE_LRAND48 || (OS2 && HAVE_RANDOM)
#define PHP_RAND_MAX 2147483647
#else
#define PHP_RAND_MAX RAND_MAX
#endif

/* {{{ proto void srand(int seed)
   Seeds random number generator */
void php3_srand(INTERNAL_FUNCTION_PARAMETERS)
{
	pval *arg;

	if (ARG_COUNT(ht) != 1 || getParameters(ht, 1, &arg) == FAILURE) {
		WRONG_PARAM_COUNT;
	}
	convert_to_long(arg);
#ifdef HAVE_SRAND48
	srand48((unsigned int) arg->value.lval);
#else
#ifdef HAVE_SRANDOM
	srandom((unsigned int) arg->value.lval);
#else
	srand((unsigned int) arg->value.lval);
#endif
#endif
}
/* }}} */

/* {{{ proto void mt_srand(int seed)
   Seeds Mersenne Twister random number generator */
void php3_mt_srand(INTERNAL_FUNCTION_PARAMETERS)
{
	pval *arg;
	if (ARG_COUNT(ht) != 1 || getParameters(ht, 1, &arg) == FAILURE) {
		WRONG_PARAM_COUNT;
	}
	convert_to_long(arg);
	seedMT(arg->value.lval);
}
/* }}} */

/* {{{ proto int rand([int min, int max])
   Returns a random number */
void php3_rand(INTERNAL_FUNCTION_PARAMETERS)
{
	pval *p_min=NULL, *p_max=NULL;
	
	switch (ARG_COUNT(ht)) {
		case 0:
			break;
		case 2:
			if (getParameters(ht, 2, &p_min, &p_max)==FAILURE) {
				RETURN_FALSE;
			}
			convert_to_long(p_min);
			convert_to_long(p_max);
			if (p_max->value.lval-p_min->value.lval <= 0) {
				php3_error(E_WARNING,"rand():  Invalid range:  %ld..%ld", p_min->value.lval, p_max->value.lval);
			} else if (p_max->value.lval-p_min->value.lval > RAND_MAX){
				php3_error(E_WARNING,"rand():  Invalid range:  %ld..%ld", p_min->value.lval, p_max->value.lval);
			}
			break;
		default:
			WRONG_PARAM_COUNT;
			break;
	}
			
	return_value->type = IS_LONG;
#ifdef HAVE_LRAND48
	return_value->value.lval = lrand48();
#else
#ifdef HAVE_RANDOM
	return_value->value.lval = random();
#else
	return_value->value.lval = rand();
#endif
#endif
    /* 
	 * A bit of tricky math here.  We want to avoid using a modulus because
	 * that simply tosses the high-order bits and might skew the distribution
	 * of random values over the range.  Instead we map the range directly.
	 *
	 * We need to map the range from 0...M evenly to the range a...b
	 * Let n = the random number and n' = the mapped random number
	 *
	 * Then we have: n' = a + n(b-a)/M
	 *
	 * We have a problem here in that only n==M will get mapped to b which
	 # means the chances of getting b is much much less than getting any of
	 # the other values in the range.  We can fix this by increasing our range
	 # artifically and using:
	 #
	 #               n' = a + n(b-a+1)/M
	 *
	 # Now we only have a problem if n==M which would cause us to produce a
	 # number of b+1 which would be bad.  So we bump M up by one to make sure
	 # this will never happen, and the final algorithm looks like this:
	 #
	 #               n' = a + n(b-a+1)/(M+1) 
	 *
	 * -RL
	 */
	if (p_min && p_max) { /* implement range */
		return_value->value.lval = p_min->value.lval +
			(int)((double)(p_max->value.lval - p_min->value.lval + 1.0) * return_value->value.lval/(PHP_RAND_MAX+1.0));
	}
}
/* }}} */

/* {{{ proto int mt_rand([int min, int max])
   Returns a random number from Mersenne Twister */
void php3_mt_rand(INTERNAL_FUNCTION_PARAMETERS)
{
	pval *p_min=NULL, *p_max=NULL;
	
	switch (ARG_COUNT(ht)) {
		case 0:
			break;
		case 2:
			if (getParameters(ht, 2, &p_min, &p_max)==FAILURE) {
				RETURN_FALSE;
			}
			convert_to_long(p_min);
			convert_to_long(p_max);
			if (p_max->value.lval-p_min->value.lval <=0)  {
				php3_error(E_WARNING,"mt_rand():  Invalid range:  %ld..%ld", p_min->value.lval, p_max->value.lval);
			}else if (p_max->value.lval-p_min->value.lval > MT_RAND_MAX){
				php3_error(E_WARNING,"mt_rand():  Invalid range:  %ld..%ld", p_min->value.lval, p_max->value.lval);
			}
			break;
		default:
			WRONG_PARAM_COUNT;
			break;
	}
			
	return_value->type = IS_LONG;
	/*
	 * Melo: hmms.. randomMT() returns 32 random bits...
	 * Yet, the previous php3_rand only returns 31 at most.
	 * So I put a right shift to loose the lsb. It *seems*
	 * better than clearing the msb. 
	 * Update: 
	 * I talked with Cokus via email and it won't ruin the algorithm
	 */
	return_value->value.lval = (long)(randomMT() >> 1);

	/* see the comment in the php3_rand() function about this ugly algorithm */
	if (p_min && p_max) { /* implement range */
		return_value->value.lval = p_min->value.lval +
			(int)((double)(p_max->value.lval - p_min->value.lval + 1.0) * return_value->value.lval/(MT_RAND_MAX+1.0));
	}
}
/* }}} */

/* {{{ proto int getrandmax(void)
   Returns the maximum value a random number can have */
void php3_getrandmax(INTERNAL_FUNCTION_PARAMETERS)
{
	return_value->type = IS_LONG;
	return_value->value.lval = PHP_RAND_MAX;
}
/* }}} */

/* {{{ proto int mt_getrandmax(void)
   Returns the maximum value a random number from Mersenne Twister can have */
void php3_mt_getrandmax(INTERNAL_FUNCTION_PARAMETERS)
{
	return_value->type = IS_LONG;
	/*
	 * Melo: it could be 2^^32 but we only use 2^^31 to maintain
	 * compatibility with the previous php3_rand
	 */
  	return_value->value.lval = MT_RAND_MAX;	/* 2^^31 */
}
/* }}} */

/*
 * Local variables:
 * tab-width: 4
 * c-basic-offset: 4
 * End:
 */