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random.s
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random.s
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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/>.
*/
#include "m74cfg.h"
.section .bss
.equ v_num, MEM_LOC_A ; Current PRNG state
.section .text
/*
** Gets next number of sequence. For asm use, r22 and r23 are clobbered.
**
** Returns in r25:r24.
*/
.global random_get
random_get:
lds r24, v_num + 0
lds r25, v_num + 1
lsl r24
rol r25
ldi r22, 0x25
ldi r23, 0x7F
adc r24, r22
adc r25, r23
ldi r22, 0xDB
eor r24, r22
sts v_num + 0, r24
sts v_num + 1, r25
ret