path: root/contrib/libs/poco/Foundation/src/Random.cpp

// 
// Random.cpp 
// 
// Library: Foundation 
// Package: Crypt 
// Module:  Random 
// 
// Definition of class Random. 
// 
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH. 
// and Contributors. 
// 
// SPDX-License-Identifier:	BSL-1.0 
// 
// 
// Based on the FreeBSD random number generator. 
// src/lib/libc/stdlib/random.c,v 1.25  
// 
// Copyright (c) 1983, 1993 
// The Regents of the University of California.  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. 
// 4. Neither the name of the University nor the names of its contributors 
//    may be used to endorse or promote products derived from this software 
//    without specific prior written permission. 
// 
// THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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 "Poco/Random.h" 
#include "Poco/RandomStream.h" 
#include <ctime> 
#if defined(_WIN32_WCE) && _WIN32_WCE < 0x800 
#error #include "wce_time.h" 
#endif 
 
 
/* 
 * random.c: 
 * 
 * An improved random number generation package.  In addition to the standard 
 * rand()/srand() like interface, this package also has a special state info 
 * interface.  The initstate() routine is called with a seed, an array of 
 * bytes, and a count of how many bytes are being passed in; this array is 
 * then initialized to contain information for random number generation with 
 * that much state information.  Good sizes for the amount of state 
 * information are 32, 64, 128, and 256 bytes.  The state can be switched by 
 * calling the setstate() routine with the same array as was initiallized 
 * with initstate().  By default, the package runs with 128 bytes of state 
 * information and generates far better random numbers than a linear 
 * congruential generator.  If the amount of state information is less than 
 * 32 bytes, a simple linear congruential R.N.G. is used. 
 * 
 * Internally, the state information is treated as an array of uint32_t's; the 
 * zeroeth element of the array is the type of R.N.G. being used (small 
 * integer); the remainder of the array is the state information for the 
 * R.N.G.  Thus, 32 bytes of state information will give 7 ints worth of 
 * state information, which will allow a degree seven polynomial.  (Note: 
 * the zeroeth word of state information also has some other information 
 * stored in it -- see setstate() for details). 
 * 
 * The random number generation technique is a linear feedback shift register 
 * approach, employing trinomials (since there are fewer terms to sum up that 
 * way).  In this approach, the least significant bit of all the numbers in 
 * the state table will act as a linear feedback shift register, and will 
 * have period 2^deg - 1 (where deg is the degree of the polynomial being 
 * used, assuming that the polynomial is irreducible and primitive).  The 
 * higher order bits will have longer periods, since their values are also 
 * influenced by pseudo-random carries out of the lower bits.  The total 
 * period of the generator is approximately deg*(2**deg - 1); thus doubling 
 * the amount of state information has a vast influence on the period of the 
 * generator.  Note: the deg*(2**deg - 1) is an approximation only good for 
 * large deg, when the period of the shift is the dominant factor. 
 * With deg equal to seven, the period is actually much longer than the 
 * 7*(2**7 - 1) predicted by this formula. 
 * 
 * Modified 28 December 1994 by Jacob S. Rosenberg. 
 * The following changes have been made: 
 * All references to the type u_int have been changed to unsigned long. 
 * All references to type int have been changed to type long.  Other 
 * cleanups have been made as well.  A warning for both initstate and 
 * setstate has been inserted to the effect that on Sparc platforms 
 * the 'arg_state' variable must be forced to begin on word boundaries. 
 * This can be easily done by casting a long integer array to char *. 
 * The overall logic has been left STRICTLY alone.  This software was 
 * tested on both a VAX and Sun SpacsStation with exactly the same 
 * results.  The new version and the original give IDENTICAL results. 
 * The new version is somewhat faster than the original.  As the 
 * documentation says:  "By default, the package runs with 128 bytes of 
 * state information and generates far better random numbers than a linear 
 * congruential generator.  If the amount of state information is less than 
 * 32 bytes, a simple linear congruential R.N.G. is used."  For a buffer of 
 * 128 bytes, this new version runs about 19 percent faster and for a 16 
 * byte buffer it is about 5 percent faster. 
 */ 
 
 
/* 
 * For each of the currently supported random number generators, we have a 
 * break value on the amount of state information (you need at least this 
 * many bytes of state info to support this random number generator), a degree 
 * for the polynomial (actually a trinomial) that the R.N.G. is based on, and 
 * the separation between the two lower order coefficients of the trinomial. 
 */ 
#define	TYPE_0		0		/* linear congruential */ 
#define	BREAK_0		8 
#define	DEG_0		0 
#define	SEP_0		0 
 
#define	TYPE_1		1		/* x**7 + x**3 + 1 */ 
#define	BREAK_1		32 
#define	DEG_1		7 
#define	SEP_1		3 
 
#define	TYPE_2		2		/* x**15 + x + 1 */ 
#define	BREAK_2		64 
#define	DEG_2		15 
#define	SEP_2		1 
 
#define	TYPE_3		3		/* x**31 + x**3 + 1 */ 
#define	BREAK_3		128 
#define	DEG_3		31 
#define	SEP_3		3 
 
#define	TYPE_4		4		/* x**63 + x + 1 */ 
#define	BREAK_4		256 
#define	DEG_4		63 
#define	SEP_4		1 
 
 
namespace Poco { 
 
 
Random::Random(int stateSize) 
{ 
	poco_assert (BREAK_0 <= stateSize && stateSize <= BREAK_4); 
 
	_pBuffer = new char[stateSize]; 
#if defined(_WIN32_WCE) && _WIN32_WCE < 0x800 
	initState((UInt32) wceex_time(NULL), _pBuffer, stateSize); 
#else 
	initState((UInt32) std::time(NULL), _pBuffer, stateSize); 
#endif 
} 
 
 
Random::~Random() 
{ 
	delete [] _pBuffer; 
} 
 
 
/* 
 * Compute x = (7^5 * x) mod (2^31 - 1) 
 * wihout overflowing 31 bits: 
 *      (2^31 - 1) = 127773 * (7^5) + 2836 
 * From "Random number generators: good ones are hard to find", 
 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 
 * October 1988, p. 1195. 
 */ 
inline UInt32 Random::goodRand(Int32 x) 
{ 
	Int32 hi, lo; 
 
	if (x == 0) x = 123459876; 
	hi = x / 127773; 
	lo = x % 127773; 
	x = 16807 * lo - 2836 * hi; 
	if (x < 0) x += 0x7FFFFFFF; 
 
	return x; 
} 
 
 
/* 
 * Initialize the random number generator based on the given seed.  If the 
 * type is the trivial no-state-information type, just remember the seed. 
 * Otherwise, initializes state[] based on the given "seed" via a linear 
 * congruential generator.  Then, the pointers are set to known locations 
 * that are exactly rand_sep places apart.  Lastly, it cycles the state 
 * information a given number of times to get rid of any initial dependencies 
 * introduced by the L.C.R.N.G.  Note that the initialization of randtbl[] 
 * for default usage relies on values produced by this routine. 
 */ 
void Random::seed(UInt32 x) 
{ 
	int i, lim; 
 
	_state[0] = x; 
	if (_randType == TYPE_0) 
		lim = NSHUFF; 
	else  
	{ 
		for (i = 1; i < _randDeg; i++) 
			_state[i] = goodRand(_state[i - 1]); 
		_fptr = &_state[_randSep]; 
		_rptr = &_state[0]; 
		lim = 10 * _randDeg; 
	} 
	for (i = 0; i < lim; i++) 
		next(); 
} 
 
 
/* 
 * Many programs choose the seed value in a totally predictable manner. 
 * This often causes problems.  We seed the generator using the much more 
 * secure random(4) interface.  Note that this particular seeding 
 * procedure can generate states which are impossible to reproduce by 
 * calling srandom() with any value, since the succeeding terms in the 
 * state buffer are no longer derived from the LC algorithm applied to 
 * a fixed seed. 
 */ 
void Random::seed() 
{ 
	std::streamsize len; 
 
	if (_randType == TYPE_0) 
		len = sizeof _state[0]; 
	else 
		len = _randDeg * sizeof _state[0]; 
 
	RandomInputStream rstr; 
	rstr.read((char*) _state, len); 
} 
 
 
/* 
 * Initialize the state information in the given array of n bytes for future 
 * random number generation.  Based on the number of bytes we are given, and 
 * the break values for the different R.N.G.'s, we choose the best (largest) 
 * one we can and set things up for it.  srandom() is then called to 
 * initialize the state information. 
 * 
 * Note that on return from srandom(), we set state[-1] to be the type 
 * multiplexed with the current value of the rear pointer; this is so 
 * successive calls to initstate() won't lose this information and will be 
 * able to restart with setstate(). 
 * 
 * Note: the first thing we do is save the current state, if any, just like 
 * setstate() so that it doesn't matter when initstate is called. 
 * 
 * Returns a pointer to the old state. 
 * 
 * Note: The Sparc platform requires that arg_state begin on an int 
 * word boundary; otherwise a bus error will occur. Even so, lint will 
 * complain about mis-alignment, but you should disregard these messages. 
 */ 
void Random::initState(UInt32 s, char* argState, Int32 n) 
{ 
	UInt32* intArgState = (UInt32*) argState; 
 
	if (n < BREAK_0)  
	{ 
		poco_bugcheck_msg("not enough state"); 
		return; 
	} 
	if (n < BREAK_1)  
	{ 
		_randType = TYPE_0; 
		_randDeg  = DEG_0; 
		_randSep  = SEP_0; 
	}  
	else if (n < BREAK_2)  
	{ 
		_randType = TYPE_1; 
		_randDeg  = DEG_1; 
		_randSep  = SEP_1; 
	}  
	else if (n < BREAK_3)  
	{ 
		_randType = TYPE_2; 
		_randDeg  = DEG_2; 
		_randSep  = SEP_2; 
	}  
	else if (n < BREAK_4)  
	{ 
		_randType = TYPE_3; 
		_randDeg  = DEG_3; 
		_randSep  = SEP_3; 
	}  
	else  
	{ 
		_randType = TYPE_4; 
		_randDeg = DEG_4; 
		_randSep = SEP_4; 
	} 
	_state  = intArgState + 1; /* first location */ 
	_endPtr = &_state[_randDeg];	/* must set end_ptr before seed */ 
	seed(s); 
	if (_randType == TYPE_0) 
		intArgState[0] = _randType; 
	else 
		intArgState[0] = MAX_TYPES * (int) (_rptr - _state) + _randType; 
} 
 
 
/* 
 * Next: 
 * 
 * If we are using the trivial TYPE_0 R.N.G., just do the old linear 
 * congruential bit.  Otherwise, we do our fancy trinomial stuff, which is 
 * the same in all the other cases due to all the global variables that have 
 * been set up.  The basic operation is to add the number at the rear pointer 
 * into the one at the front pointer.  Then both pointers are advanced to 
 * the next location cyclically in the table.  The value returned is the sum 
 * generated, reduced to 31 bits by throwing away the "least random" low bit. 
 * 
 * Note: the code takes advantage of the fact that both the front and 
 * rear pointers can't wrap on the same call by not testing the rear 
 * pointer if the front one has wrapped. 
 * 
 * Returns a 31-bit random number. 
 */ 
UInt32 Random::next() 
{ 
	UInt32 i; 
	UInt32 *f, *r; 
 
	if (_randType == TYPE_0)  
	{ 
		i = _state[0]; 
		_state[0] = i = goodRand(i) & 0x7FFFFFFF; 
	}  
	else  
	{ 
		/* 
		 * Use local variables rather than static variables for speed. 
		 */ 
		f = _fptr; r = _rptr; 
		*f += *r; 
		i = (*f >> 1) & 0x7FFFFFFF;	/* chucking least random bit */ 
		if (++f >= _endPtr) { 
			f = _state; 
			++r; 
		} 
		else if (++r >= _endPtr) { 
			r = _state; 
		} 
 
		_fptr = f; _rptr = r; 
	} 
	return i; 
} 
 
 
} // namespace Poco