/*
 * $Id: amiga_rangerand.c,v 1.3 2006-01-08 12:04:22 obarthel Exp $
 *
 * :ts=4
 *
 * Portable ISO 'C' (1994) runtime library for the Amiga computer
 * Copyright (c) 2002-2015 by Olaf Barthel <obarthel (at) gmx.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Neither the name of Olaf Barthel nor the names of contributors
 *     may be used to endorse or promote products derived from this
 *     software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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 <exec/types.h>

/****************************************************************************/

#include <clib/alib_protos.h>

/****************************************************************************/

ULONG RangeSeed;

/****************************************************************************/

UWORD
RangeRand(ULONG max_value)
{
	ULONG next_value;
	ULONG result;
	ULONG value;
	UWORD range;
	UWORD bits;

	range = (max_value & 0xFFFF);
	bits = range - 1;

	value = RangeSeed;

	do
	{
		next_value = value + value;
		if(next_value <= value)
			next_value ^= 0x1D872B41;

		value = next_value;

		bits = bits >> 1;
	}
	while(bits != 0);

	RangeSeed = value;

	if(range == 0)
		result = value & 0xFFFF;
	else
		result = (range * (value & 0xFFFF)) >> 16;

	return((UWORD)result);
}