DOS ain't dead - trip report: Tiny C Compiler 0.9.27

trip report: Tiny C Compiler 0.9.27 (Miscellaneous)

posted by tkchia , 05.02.2026, 23:13

Hello bencollver,

Glad you are making progress. :-)

> When c = 0xfffffff8, TCC takes the "short reference" branch while Watcom
> takes the "else" branch. What is this if statement actually
> testing?

TCC directly generates machine code, and this is apparently where it emits a ModR/M byte and an address displacement for certain operand pairs (e.g. -0x10(%ebp), %eax).

The conditional is supposed to test if the displacement (here -0x10) is in the range -128 to +127. If it is, then TCC can opt to encode a short 1-byte displacement rather than a 4-byte one.

Thank you!

---
https://codeberg.org/tkchia · https://disroot.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

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Complete thread:

trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 17:02 (Miscellaneous)
- trip report: Tiny C Compiler 0.9.27 - tkchia, 04.02.2026, 17:55
  - trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 18:48
    - trip report: Tiny C Compiler 0.9.27 - Japheth, 04.02.2026, 21:12
      - trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 21:44
      - trip report: Tiny C Compiler 0.9.27 - bretjohn, 05.02.2026, 22:24
        trip report: Tiny C Compiler 0.9.27 - Rugxulo, 05.02.2026, 23:09
        trip report: Tiny C Compiler 0.9.27 - bretjohn, 06.02.2026, 01:59
    - trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 21:38
      - trip report: Tiny C Compiler 0.9.27 - tkchia, 05.02.2026, 16:44
        trip report: Tiny C Compiler 0.9.27 - bencollver, 05.02.2026, 18:34
        trip report: Tiny C Compiler 0.9.27 - bencollver, 05.02.2026, 22:22
        trip report: Tiny C Compiler 0.9.27 - tkchia, 05.02.2026, 23:13
        trip report: Tiny C Compiler 0.9.27 - Rugxulo, 05.02.2026, 23:16
        trip report: Tiny C Compiler 0.9.27 - tkchia, 05.02.2026, 23:18
        trip report: Tiny C Compiler 0.9.27 - tkchia, 06.02.2026, 23:45
- trip report: Tiny C Compiler 0.9.27 - bencollver, 11.02.2026, 00:44
  - trip report: Tiny C Compiler 0.9.27 - Rugxulo, 11.02.2026, 01:42
    - trip report: Tiny C Compiler 0.9.27 - bencollver, 11.02.2026, 02:06