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A comment on A 28-byte “hello, world” program assembled with DEBUG.EXE in MS-DOS. Parent comment

Re:A 28-byte “hello, world” program assembled with DEBUG.EXE... by ralferoo on Sunday October 30, 2022 @06:11PM (#33399395)
Not a size optimisation, but a performance optimisation...

  INT 21
  RET
can be replaced with

  JP 5
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Re:A 28-byte “hello, world” program assembled with DEBUG.EXE... by blueflow on Sunday October 30, 2022 @07:02PM (#33399952)
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.

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Re:A 28-byte “hello, world” program assembled with DEBUG.EXE... by jart on Monday October 31, 2022 @01:33AM (#33402389)
Jump parity? But according to http://www.fysnet.net/yourhelp.htm the parity flag is only set in DOS 7.1+
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