From: krishna.myneni@ccreweb.org   
      
   On 3/4/24 11:24, Anton Ertl wrote:   
   > Many years ago I have read here about Forth systems where DO and ?DO   
   > push three items on the return stack: the two values from the data   
   > stack (initial index and limit) like many other Forth systems, but in   
   > addition they also push the address that LOOP/+LOOP later jumps to.   
   >   
   > I used to consider this to be inefficient, but it turns out that in an   
   > efficient interpreter-based Forth system like, say gforth-fast from   
   > 2022 it would actually be more efficient than compiling that address   
   > with the (LOOP)/(+LOOP) and loading it from there.   
   >   
   > My question is: Which Forth systems have a DO/?DO that pushes the   
   > address that LOOP/+LOOP then jumps to?   
   >   
   > - anton   
      
   Yes, kForth uses this method. DO pushes three items onto the return   
   stack, the two loop parameters, and the virtual instruction pointer.   
      
   \ From ForthVM.cpp   
      
   int CPP_do ()   
   {   
      // stack: ( -- | generate opcodes for beginning of loop structure )   
      
      pCurrentOps->push_back(OP_PUSH);   
      pCurrentOps->push_back(OP_PUSH);   
      pCurrentOps->push_back(OP_PUSHIP);   
      
      dostack.push(pCurrentOps->size());   
      return 0;   
   }   
      
   --   
   Krishna   
      
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