5 ms·

Not a size optimisation, but a performance optimisation... INT 21 RET can be replaced with JP 5

• blueflow 4y ago
  That mnemonic would be "JMP" on x86. At address 5 in the PSP is the CP/M-style syscall entry point, it is not advised to not use it because it relies on the A20 line being short-circuited to zero, which cannot be relied on in later MS-DOS versions. I don't see why this would be faster than using RET directly and having the INT 20 opcode at address 0 do the work.
• jart 4y ago
  Jump parity? But according to http://www.fysnet.net/yourhelp.htm http://www.fysnet.net/yourhelp.htm the parity flag is only set in DOS 7.1+