mirror of https://github.com/trudnai/Steve2.git
127 lines
3.3 KiB
C
127 lines
3.3 KiB
C
//
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// main.c
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// 6502
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//
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// Created by Tamas Rudnai on 7/14/19.
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// Copyright © 2019 GameAlloy. All rights reserved.
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//
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#ifndef __6502_INSTR_ARITHMETIC_H__
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#define __6502_INSTR_ARITHMETIC_H__
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#include "common.h"
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/**
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ADC Add Memory to Accumulator with Carry
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A + M + C -> A, C N Z C I D V
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+ + + - - +
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addressing assembler opc bytes cyles
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--------------------------------------------
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immidiate ADC #oper 69 2 2
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zeropage ADC oper 65 2 3
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zeropage,X ADC oper,X 75 2 4
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absolute ADC oper 6D 3 4
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absolute,X ADC oper,X 7D 3 4*
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absolute,Y ADC oper,Y 79 3 4*
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(indirect,X) ADC (oper,X) 61 2 6
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(indirect),Y ADC (oper),Y 71 2 5*
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**/
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INLINE void ADC( uint8_t src ) {
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dbgPrintf("ADC(%02X) ", src);
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uint16_t tmp;
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// V = C7 != C6
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m6502.V = ((m6502.A & 0x7F) + (src & 0x7F) + m6502.C) > 0x7F;
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if ( m6502.D ) {
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if ( (tmp = (m6502.A & 0x0F) + (src & 0x0F) + m6502.C) > 0x09 ) {
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tmp += 0x06;
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}
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if ( (tmp += (m6502.A & 0xF0) + (src & 0xF0)) > 0x99 ) {
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tmp += 0x60;
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}
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// tmp = m6502.A + src + m6502.C;
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//
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// if ( (tmp & 0x0F) > 0x09 ) {
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// tmp += 0x06;
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// }
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// if ( tmp > 0x99 ) {
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// tmp += 0x60;
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// }
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}
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else {
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tmp = (uint16_t)m6502.A + src + m6502.C;
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}
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set_flags_NZ( m6502.A = tmp );
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m6502.C = tmp > 0xFF;
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m6502.V ^= m6502.C;
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// // this is good but slow:
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// uint16_t tmp = (uint16_t)m6502.A + src + m6502.C;
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// m6502.V = ( !((m6502.A ^ src) & 0x80)) && ( (m6502.A ^ tmp) & 0x80);
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// m6502.C = tmp > 0xFF;
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// set_flags_NZ( m6502.A = tmp );
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// // this is good but slow:
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// uint16_t tmp = (uint16_t)m6502.A + src + m6502.C;
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// m6502.V = ( ((m6502.A ^ src) ^ (m6502.A ^ tmp)) & 0x80 ) != 0;
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// m6502.C = tmp > 0xFF;
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// set_flags_NZ( m6502.A = tmp );
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}
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/**
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SBC Subtract Memory from Accumulator with Borrow
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A - M - C -> A N Z C I D V
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+ + + - - +
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addressing assembler opc bytes cyles
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--------------------------------------------
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immidiate SBC #oper E9 2 2
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zeropage SBC oper E5 2 3
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zeropage,X SBC oper,X F5 2 4
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absolute SBC oper ED 3 4
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absolute,X SBC oper,X FD 3 4*
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absolute,Y SBC oper,Y F9 3 4*
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(indirect,X) SBC (oper,X) E1 2 6
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(indirect),Y SBC (oper),Y F1 2 5*
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**/
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INLINE void SBC( uint8_t src ) {
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dbgPrintf("SBC(%02X) ", src);
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// ADC( ~src );
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uint16_t tmp;
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if( m6502.D ) {
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tmp = (m6502.A & 0x0F) - ( src & 0x0F ) - !m6502.C;
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if( (tmp & 0x10) != 0) {
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tmp = ( (tmp - 0x06 ) & 0x0F ) | ( (m6502.A & 0xF0) - (src & 0xF0) - 0x10 );
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}
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else {
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tmp = (tmp & 0x0F) | ( (m6502.A & 0xF0) - (src & 0xF0) );
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}
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if(( tmp & 0x100 ) != 0) {
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tmp -= 0x60;
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}
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}
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else
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{
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tmp = m6502.A - src - !m6502.C;
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}
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m6502.C = tmp < 0x100;
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m6502.V = ( (m6502.A ^ tmp) & 0x80 ) && ( (m6502.A ^ src) & 0x80 );
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set_flags_NZ( m6502.A = tmp );
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}
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#endif // __6502_INSTR_ARITHMETIC_H__
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