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It appears that file checksums are not reliable.

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This commit is contained in:
Thomas Harte 2019-07-17 14:56:50 -04:00
parent b9a34bee51
commit 77333ff9f7
1 changed files with 15 additions and 3 deletions
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18
Storage/Disk/DiskImage/Formats/MacintoshIMG.cpp
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@ -106,15 +106,27 @@ MacintoshIMG::MacintoshIMG(const std::string &file_name) :
const auto computed_data_checksum = checksum(data_);
const auto computed_tag_checksum = checksum(tags_, 12);
if(computed_tag_checksum != tag_checksum || computed_data_checksum != data_checksum)
throw Error::InvalidFormat;
/*
Yuck! It turns out that at least some disk images have incorrect checksums,
and other emulators accept them regardless. So this test is disabled, at least
for now. It'd probably be smarter to accept the disk image as provisionally
incorrect and somehow communicate the issue to the user? Or, much better,
verify the filesystem if the checksums don't match.
*/
(void)data_checksum;
(void)computed_data_checksum;
(void)tag_checksum;
(void)computed_tag_checksum;
// if(computed_tag_checksum != tag_checksum || computed_data_checksum != data_checksum)
// throw Error::InvalidFormat;
}
}
uint32_t MacintoshIMG::checksum(const std::vector<uint8_t> &data, size_t bytes_to_skip) {
uint32_t result = 0;
// Checksum algorith is: take each two bytes as a big-endian word; add that to a
// Checksum algorithm is: take each two bytes as a big-endian word; add that to a
// 32-bit accumulator and then rotate the accumulator right one position.
for(size_t c = bytes_to_skip; c < data.size(); c += 2) {
const uint16_t next_word = uint16_t((data[c] << 8) | data[c+1]);