SvarDOS
INT21,36 handler scales numers wrong
Affected file: drdos/disk.asm Routine: func36 Reference: https://fd.lod.bz/rbil/interrup/dos_kernel/2136.html
When operating on a drive with either more than 0xffff total clusters or 0xffff clusters free, the code tries to adapt the the values by shifting the cluster numbers to the right and shifting the sectors per cluster to the left. However, only the clusters free is taken into account and scaled, making the total clusters value wrong if a shift is made.
Also, it should be made sure that the values returned via AX*BC*CX and AX*CX*DX fit within 32 bits. This is because software calling this routine could calculate value with 32-bit arithmetic, and then would cause an overflow.
First noticed in https://github.com/SvarDOS/edrdos/issues/128#issuecomment-2581291697
Fixed partially by https://hg.pushbx.org/ecm/edrdos/rev/ec560d130824
The fitting within 32-bit arithmetic is not ensured by this if the bpc is >32 KiB to begin with (before the loop).