[TUHS] CRC calculation in the 1980s

segaloco via TUHS tuhs at tuhs.org
Tue Sep 19 10:02:50 AEST 2023

> Any suggestions as to why the on-the-fly algorithm did not catch on more in the 1980’s? Maybe it was simply less well known than I think?

The CRC algorithm I'm familiar with shows up in Dragon Quest for the Famicom in 1986[1], written in 6502 assembly.  Admittedly though I only recognized it due to the EOR with 0x1021 on lines 318-323.  That I then only know from a quick and dirty CRC I threw in an XMODEM-CRC client [2] I did to accommodate for a bug in the JH7100 RISC-V board's recovery ROM implementation.  Not sure if this is along the lines of the approach you're talking about, admittedly these two instances are literally all I know about CRC, just enough to be dangerous :)

Still, a concrete example of ChunSoft's 6502 CRC calculation in the mid 80s, if that helps with the assessment of the time period/flow of ideas in the industry.

- Matt G.

[1] - https://gitlab.com/segaloco/dq1disasm/-/blob/master/src/chr3/start_pw.s
[2] - https://gitlab.com/segaloco/riscv-bits/-/blob/master/util/sxj.c

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