Fix: incorrect setting of UD_ACLU when freeing a FAT chain #96
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When freeing a FAT chain (while deleting a file) the UD_ACLU value of the unit descriptor, which holds the smaller free cluster number, is updated to the smallest cluster number freed. The code doing this had a bug and instead, a random memory address was modified; for small cluster numbers this meant that the Nextor code itself was overwritten and this caused the computer to crash. This commit fixes that.
theNestruo
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Jan 13, 2022
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Konamiman
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Mar 22, 2022
vipoo
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Oct 4, 2023
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Nextor 2.1.1 Alpha 1 introduced a new mechanism to improve the performance of cluster chain allocation in large drives, by caching the value of the smallest free cluster number (#68 and #72).
There's however a problem. When freeing a FAT chain (while deleting a file) the value of the cached value in the unit descriptor of the drive is updated to the smallest cluster number freed, but the code doing this has a bug and instead, a random memory address is modified; for small cluster numbers this means that the Nextor code itself is overwritten and this caused the computer to crash.
This pull request fixes this problem. To test the fix, you can use an empty floppy/storage device (or an equivalent disk image in an emulator); creating and deleting a few files will end up causing a computer crash in Nextor 2.1.1 beta 1, which shouldn't happen when this fix is applied.