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random.h
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random.h
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/*
* Dragon - Simple 16 bit full sequence PRNG
* Copyright (C) 2016 Sandor Zsuga (Jubatian)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* 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 the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
** A simple 16 bit full sequence PRNG, using the "5 byte PRNG" concept.
**
** The base concept is as follows:
**
** lsl reg
** adc reg, NUM1
** eor reg, NUM2
**
** This on a 6502 takes 5 bytes, and iterates "reg" in a pseudorandom manner
** over all 256 possible values with the right NUM1 and NUM2 combination.
**
** This PRNG here is a 16 bit adaptation with the following constants:
**
** NUM1 = 0x7F25
** NUM2 = 0x00DB
**
** This is the best full sequence where NUM2 is below 256.
**
** No seeding is provided, variation may be ensured by a dummy fetch in every
** frame (so the unpredictable timing of the user's actions will ensure
** variation).
*/
#ifndef RANDOM_H
#define RANDOM_H
#include "types.h"
/*
** Gets next number of sequence. For asm use, r22 and r23 are clobbered.
*/
uint16 random_get(void);
#endif