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There's only *three* bytes of prologue in an Apple 2 data record. Sigh. Good

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reads off at least one Kryoflux dump, now.
This commit is contained in:
David Given
2019-03-02 13:46:54 +01:00
parent 9d24bc54d8
commit b2af838ca5
1 changed files with 8 additions and 10 deletions
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18
lib/apple2/decoder.cc
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@@ -32,23 +32,21 @@ static std::vector<uint8_t> decode_crazy_data(const uint8_t* inp, int& status)
uint8_t checksum = 0;
for (unsigned i = 0; i < APPLE2_ENCODED_SECTOR_LENGTH; i++)
{
uint8_t b = decode_data_gcr(*inp++);
uint8_t newvalue = b ^ checksum;
checksum ^= decode_data_gcr(*inp++);
if (i >= 0x56)
if (i >= 86)
{
/* 6 bit */
output[i - 0x56] |= (newvalue << 2);
output[i - 86] |= (checksum << 2);
}
else
{
/* 3 * 2 bit */
output[i + 0x00] = ((newvalue >> 1) & 0x01) | ((newvalue << 1) & 0x02);
output[i + 0x56] = ((newvalue >> 3) & 0x01) | ((newvalue >> 1) & 0x02);
if ((i + 0xAC) < APPLE2_SECTOR_LENGTH)
output[i + 0xAC] = ((newvalue >> 5) & 0x01) | ((newvalue >> 3) & 0x02);
output[i + 0] = ((checksum >> 1) & 0x01) | ((checksum << 1) & 0x02);
output[i + 86] = ((checksum >> 3) & 0x01) | ((checksum >> 1) & 0x02);
if ((i + 172) < APPLE2_SECTOR_LENGTH)
output[i + 172] = ((checksum >> 5) & 0x01) | ((checksum >> 3) & 0x02);
}
checksum = newvalue;
}
checksum &= 0x3f;
@@ -100,7 +98,7 @@ SectorVector Apple2Decoder::decodeToSectors(
std::vector<uint8_t> clippedbytes(rawbytes);
clippedbytes.resize(APPLE2_ENCODED_SECTOR_LENGTH + 5);
int status = Sector::BAD_CHECKSUM;
auto data = decode_crazy_data(&clippedbytes[4], status);
auto data = decode_crazy_data(&clippedbytes[3], status);
auto sector = std::unique_ptr<Sector>(
new Sector(status, nextTrack, 0, nextSector, data));