Post #636109

2026-02-06 20:19 UTC

A visualisation of the 68000 instruction set. This 512x128 image encodes each of the 65536 possible opodes in the first word of the instruction. Each different colour maps to a different signature of operand/size decoding. For example, you can see the Line-A and Line-F instructions as the horizontal blocks of green right the way across the image. (Generated from one of the tools I&#39;m using to create a disassembler) #atari

Replies (3)

@tattlemuss@mastodon.gamedev.place 2026-02-06 22:03

the purpose of this exercise is to compress my decode table -- I don't want a 64K array of decoder function indices. The previous image showed that there is 2D structure in the bit pattern -- every 512 values there is repetition. In this image I swizzle the opcode values using bitshifts, and making each row 64 values wide. It turns out that 75% of the 1024 rows always have the same value in every column. This should allow me to shrink the table to about 17.4K with a simple lookup.

Open ##1943913
@gunstick@mastodon.opencloud.lu 2026-02-06 21:48

@tattlemuss In had now an idea of a flicker animation which will highlight the pixel of the currently executing instruction inside of hatari.

Open ##1943915
@questor@mastodon.gamedev.place 2026-02-09 08:54

@tattlemuss faszinating to visualize code to see patterns in it to optimize.... great idea!

Open ##1943918