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Revamp how extra zeros are handled

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It's not OK to call seek() here. Instead, add a function which can read
an apple 8-bit flux value in terms of readRaw8 and readRawBits. Apply
this function to all the data bytes, rather than just the first one.
This commit is contained in:
Jeff Epler
2022-03-02 07:45:24 -06:00
parent 386d22a45e
commit 79eec41bcd
1 changed files with 19 additions and 5 deletions
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24
arch/apple2/decoder.cc
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@@ -114,14 +114,28 @@ public:
// as it was a '1' reaching the top bit of a shift register
// that triggered a byte to be available, but it affects the
// way the data is read here.
auto p = tell();
auto b = readRawBits(1);
if(b[0]) seek(p);
//
// While the floppies tested only seemed to need this applied
// to the first byte of the data record, applying it
// consistently to all of them doesn't seem to hurt, and
// simplifies the code.
/* Read and decode data. */
unsigned recordLength = APPLE2_ENCODED_SECTOR_LENGTH + 2;
Bytes bytes = toBytes(readRawBits(recordLength*8)).slice(0, recordLength);
auto readApple8 = [&]() {
auto result = readRaw8();
while(result & 0x80 == 0) {
auto b = readRawBits(1);
result = (result << 1) | b[0];
}
return result;
};
constexpr unsigned recordLength = APPLE2_ENCODED_SECTOR_LENGTH + 2;
uint8_t bytes[recordLength];
for(auto &byte : bytes) {
byte = readApple8();
}
// Upgrade the sector from MISSING to BAD_CHECKSUM.
// If decode_crazy_data succeeds, it upgrades the sector to