From: quadibloc@invalid.invalid   
      
   On Sun, 31 Aug 2025 06:17:07 +0000, John Savard wrote:   
      
   > Instead of a block header being used to indicate code consisting of   
   > variable-length instructions, variable-length instructions would be   
   > contained within a sequence of pairs of 32-bit instructions of this   
   > form:   
   >   
   > 11110xx(17 bits)(8 bits)   
   > 11111x(9 bits)(17 bits)   
      
   Making the basic unit 17 bits without externally indicating the   
   instruction length prevents a full 17-bit short instruction.   
      
   As this is inadequate, I considered abandoning the dream of Concertina III.   
      
   However, if I use both major chunks of opcode space formerly used for   
   headers or other items to be dropped, I can do this:   
      
   101xx(18 bits)(9 bits)   
   1111x(9 bits)(18 bits)   
      
   which means, though, that I now have to use a longer prefix portion on the   
   instructions with immediates, and this may possibly prevent them from   
   working out properly.   
      
   I also have 111001 available, a prefix of only 6 bits. If I use that for   
   immediates, how will it work out?   
      
   111010(10 bits)(16 bits)   
   111011(10 bits)(16 bits)   
      
   ...20 bits of instruction, for 32 bits of immediate. Since the instruction   
   proper needs 7 bits of opcode plus 5 bits of destination register, that   
   leaves 8 bits to distinguish the instruction from other kinds of   
   instruction with these prefixes. So far, so good.   
      
   111010(10 bits)(16 bits)   
   111011(2 bits)(24 bits)   
   111011(2 bits)(24 bits)   
      
   Fitting a 64-bit immediate into three words (rather than four) is also   
   still doable. It takes 1/4 of the available opcode space - but that's OK,   
   because nothing else has a similar problem, not 48-bit immediates, and not   
   128-bit immediates.   
      
   The only thing I do lose is being able to also have, as I had only very   
   recently introduced to Concertina II, the use of the 64-bit immediate   
   structure to have memory-reference instructions with 64-bit absolute   
   addresses.   
      
   John Savard   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)