mirror of
https://github.com/davidgiven/fluxengine.git
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102 lines
2.3 KiB
C++
102 lines
2.3 KiB
C++
#include "globals.h"
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#include "record.h"
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#include "decoders/decoders.h"
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#include "amiga.h"
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#include "bytes.h"
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#include "fmt/format.h"
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uint32_t amigaChecksum(const Bytes& bytes)
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{
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ByteReader br(bytes);
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uint32_t checksum = 0;
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assert((bytes.size() & 3) == 0);
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while (!br.eof())
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checksum ^= br.read_be32();
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return checksum & 0x55555555;
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}
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static uint8_t everyother(uint16_t x)
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{
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/* aabb ccdd eeff gghh */
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x &= 0x6666; /* 0ab0 0cd0 0ef0 0gh0 */
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x >>= 1; /* 00ab 00cd 00ef 00gh */
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x |= x << 2; /* abab cdcd efef ghgh */
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x &= 0x3c3c; /* 00ab cd00 00ef gh00 */
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x >>= 2; /* 0000 abcd 0000 efgh */
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x |= x >> 4; /* 0000 abcd abcd efgh */
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return x;
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}
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Bytes amigaInterleave(const Bytes& input)
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{
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Bytes output;
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ByteWriter bw(output);
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/* Write all odd bits. (Numbering starts at 0...) */
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{
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ByteReader br(input);
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while (!br.eof())
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{
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uint16_t x = br.read_be16();
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x &= 0xaaaa; /* a0b0 c0d0 e0f0 g0h0 */
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x |= x >> 1; /* aabb ccdd eeff gghh */
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x = everyother(x); /* 0000 0000 abcd efgh */
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bw.write_8(x);
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}
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}
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/* Write all even bits. */
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{
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ByteReader br(input);
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while (!br.eof())
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{
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uint16_t x = br.read_be16();
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x &= 0x5555; /* 0a0b 0c0d 0e0f 0g0h */
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x |= x << 1; /* aabb ccdd eeff gghh */
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x = everyother(x); /* 0000 0000 abcd efgh */
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bw.write_8(x);
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}
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}
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return output;
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}
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Bytes amigaDeinterleave(const uint8_t*& input, size_t len)
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{
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assert(!(len & 1));
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const uint8_t* odds = &input[0];
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const uint8_t* evens = &input[len/2];
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Bytes output;
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ByteWriter bw(output);
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for (size_t i=0; i<len/2; i++)
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{
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uint8_t o = *odds++;
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uint8_t e = *evens++;
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/* This is the 'Interleave bits with 64-bit multiply' technique from
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* http://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
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*/
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uint16_t result =
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(((e * 0x0101010101010101ULL & 0x8040201008040201ULL)
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* 0x0102040810204081ULL >> 49) & 0x5555) |
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(((o * 0x0101010101010101ULL & 0x8040201008040201ULL)
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* 0x0102040810204081ULL >> 48) & 0xAAAA);
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bw.write_be16(result);
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}
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input += len;
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return output;
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}
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Bytes amigaDeinterleave(const Bytes& input)
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{
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const uint8_t* ptr = input.cbegin();
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return amigaDeinterleave(ptr, input.size());
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}
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