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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 dmitrygr on Sunday October 30, 2022 @04:44PM (#33398465)
You are right and sister comment to this one is wrong. Thusly:

MOV AH, 9

MOV DX, str

INT 21

MOV AH, 0

INT 21

Str:

DB 'hello, world', d, A, '$'

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Re:A 28-byte “hello, world” program assembled with DEBUG.EXE... by q-big on Sunday October 30, 2022 @05:09PM (#33398738)
This program can be simplified further:

  MOV AH, 9
  MOV DX, str
  INT 21
  RET
  str:
  DB 'hello, world', d, A, '$'
Why can

  MOV AH, 0
  INT 21
be replaced by RET? Here is the answer: https://stackoverflow.com/a/60805758

UPDATE: Under https://news.ycombinator.com/item?id=33398592 userbinator posted an additional possible optimization.

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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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