Re: Understanding the x18 instruction jump table
"Helen Austin" <[email protected]>
| Newsgroups | gmane.comp.lang.forth.colorforth |
|---|---|
| Message-ID | <[email protected]> |
On 6/13/06, John Drake <[email protected]> wrote: > : inst ( n ) 1 slot +! 1f and jump jmp jmp call call > jz jz jns jns @b @+ n @a !b !+ nul !a -x 2*x 2/x +* > orx andx nul +x r@ a@ t@ s@ r! a!x nul t! > > Why are the opcodes jmp, call and jns repeated? At a guess, because the LSB of those four instructions (call, jmp, jz, jns) either affects their operation or is ignored when decoding them. Note that after "1f and jump" there are exactly 32 words - one for every 5-bit opcode, I'd guess. Helpful? Regards Helen