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72 lines
2.5 KiB
C++
72 lines
2.5 KiB
C++
//
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// CommodoreGCR.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 29/07/2016.
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// Copyright 2016 Thomas Harte. All rights reserved.
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//
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#include "CommodoreGCR.hpp"
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#include <limits>
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using namespace Storage;
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Time Storage::Encodings::CommodoreGCR::length_of_a_bit_in_time_zone(unsigned int time_zone) {
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// the speed zone divides a 4Mhz clock by 13, 14, 15 or 16, with higher-numbered zones being faster (i.e. each bit taking less time)
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return Time(16 - time_zone, 4000000u);
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}
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unsigned int Storage::Encodings::CommodoreGCR::encoding_for_nibble(uint8_t nibble) {
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switch(nibble & 0xf) {
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case 0x0: return 0x0a; case 0x1: return 0x0b;
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case 0x2: return 0x12; case 0x3: return 0x13;
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case 0x4: return 0x0e; case 0x5: return 0x0f;
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case 0x6: return 0x16; case 0x7: return 0x17;
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case 0x8: return 0x09; case 0x9: return 0x19;
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case 0xa: return 0x1a; case 0xb: return 0x1b;
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case 0xc: return 0x0d; case 0xd: return 0x1d;
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case 0xe: return 0x1e; case 0xf: return 0x15;
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// for the benefit of the compiler; clearly unreachable
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default: return 0xff;
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}
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}
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unsigned int Storage::Encodings::CommodoreGCR::decoding_from_quintet(unsigned int quintet) {
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switch(quintet & 0x1f) {
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case 0x0a: return 0x0; case 0x0b: return 0x1;
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case 0x12: return 0x2; case 0x13: return 0x3;
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case 0x0e: return 0x4; case 0x0f: return 0x5;
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case 0x16: return 0x6; case 0x17: return 0x7;
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case 0x09: return 0x8; case 0x19: return 0x9;
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case 0x1a: return 0xa; case 0x1b: return 0xb;
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case 0x0d: return 0xc; case 0x1d: return 0xd;
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case 0x1e: return 0xe; case 0x15: return 0xf;
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default: return std::numeric_limits<unsigned int>::max();
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}
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}
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unsigned int Storage::Encodings::CommodoreGCR::encoding_for_byte(uint8_t byte) {
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return encoding_for_nibble(byte) | (encoding_for_nibble(byte >> 4) << 5);
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}
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unsigned int Storage::Encodings::CommodoreGCR::decoding_from_dectet(unsigned int dectet) {
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return decoding_from_quintet(dectet) | (decoding_from_quintet(dectet >> 5) << 4);
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}
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void Storage::Encodings::CommodoreGCR::encode_block(uint8_t *destination, uint8_t *source) {
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unsigned int encoded_bytes[4] = {
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encoding_for_byte(source[0]),
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encoding_for_byte(source[1]),
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encoding_for_byte(source[2]),
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encoding_for_byte(source[3]),
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};
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destination[0] = uint8_t(encoded_bytes[0] >> 2);
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destination[1] = uint8_t((encoded_bytes[0] << 6) | (encoded_bytes[1] >> 4));
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destination[2] = uint8_t((encoded_bytes[1] << 4) | (encoded_bytes[2] >> 6));
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destination[3] = uint8_t((encoded_bytes[2] << 2) | (encoded_bytes[3] >> 8));
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destination[4] = uint8_t(encoded_bytes[3]);
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}
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