Inspired by Sandor Schneider's "STABLE" project I decided that it was time to update the code that handles the stack manipulations, particularly important for arithmetic, logical and comparison operations.

I found that a 4 level stack based on registers was not only limited but difficult to manage without a lot of time wasted shuffling registers.

Using Sandor's approach, there is an array in memory st[ ] which is accessed by a stack pointer variable s.  The top item on the stack is st[s] and the next item on the stack is st[s-1].

The only operations needed now to handle the stack are pre-increment or post-decrement the stack pointer using s++  or s--.

Here are the arithmetical instructions recoded to use this technique:

//---------------------------------------------------------------------       
//  Arithmetical, Logical and Comparison operations:   

case '+':  st[s-1]+=st[s]; s-- ;        break;    // ADD     
case '-':  st[s-1]-=st[s]; s-- ;        break;    // SUB    
case '*':  st[s-1]*=st[s]; s-- ;        break;    // MUL   
case '/':  st[s-1]/=st[s]; s-- ;        break;    // DIV
case '_':  st[s]=-st[s];                break;    // NEG

case '&':  st[s-1]&=st[s]; s-- ;        break;    // AND          
case '|':  st[s-1]|=st[s]; s-- ;        break;    // OR     
case '^':  st[s-1]^=st[s]; s-- ;        break;    // XOR      
case '~':  st[s]= ~st[s];               break;    // NOT
      
case '<':  if(st[s]> st[s-1]){st[s]=-1;}else{st[s]=0;}  break;    // LT    
case '>':  if(st[s]< st[s-1]){st[s]=-1;}else{st[s]=0;}  break;    // GT
case '=':  if(st[s]==st[s-1]){st[s]=-1;}else{st[s]=0;}  break;    // EQ

SIMPL continues to be a world of exploration.

When running on the 600MHz Teensy 4.0 it has lightning speed.

50 million empty loops per second 

9.2 million 32-bit addition or subtractions per second