C02/src/cond.c

/************************************
 * C02 Conditional Parsing Routines *
 ************************************/
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <errno.h>
#include "common.h"
#include "asm.h"
#include "parse.h"
#include "vars.h"
#include "expr.h"
#include "label.h"
#include "cond.h"

int  cmprtr;    //Encoded Comparison Operator
int  cmpenc;    //Encoded Comparator Character

/* Encode Comparison Operator Character *
 * Args: Comparison Operator Character   *
 * Returns: Comparison Operator Bit Mask */
int enccmp(char c) {
  int e;
  DEBUG("Encoding Comparison Character '%c'", c)
  switch(c) {
    case '=': e = 1; break;
    case '<': e = 2; break;
    case '>': e = 4; break;
    default:  e = 0; 
  }
  if (e) { CCMNT(c); skpchr(); }
  DETAIL(", encoded as %d\n", e);
  return e;
}

/* Process and Compile Comparison Operator and        *
 * Args: comparator - Encoded Comparison Operator     *
 * Uses: term - Term Being Compared Against           *
 *       label - Branch Target if Comparison is FALSE */
void prccmp(void) {
  DEBUG("Processing comparator %d\n", cmprtr)
  switch(cmprtr) {
    case 0: // Raw Expression (Skip)
      asmlin("BEQ", cndlbl); break;
    case 1: // = or ==
      asmlin("CMP", term); asmlin("BNE", cndlbl); break;
    case 2: // <
      asmlin("CMP", term); asmlin("BCS", cndlbl); break;
    case 3: // <= or =<
      asmlin("CLC", "");   asmlin("SBC", term);   asmlin("BCS", cndlbl); break;
    case 4: // >
      asmlin("CLC", "");   asmlin("SBC", term);   asmlin("BCC", cndlbl); break;
    case 5: // >= or =>
      asmlin("CMP", term); asmlin("BCC", cndlbl); break;
    case 6: // <> or ><
      asmlin("CMP", term); asmlin("BEQ", cndlbl); break;
    case 7: // Raw Expression (Normal)
      asmlin("BNE", cndlbl); break;
    default:
      ERROR("Unsupported comparison operator index %d\n", cmprtr, EXIT_FAILURE)
  }
}

/* Parse Comparison */
void prscmp(int revrse) {
  skpspc();
  cmpenc = enccmp(nxtchr);      //Encode Comparison Character
  cmprtr = cmpenc;              //Set Encoded Comparator 
  if (cmprtr) {
    cmpenc = enccmp(nxtchr);    //Encode Next Comparison Character
    if (cmpenc != 0) cmprtr = cmprtr | cmpenc; //Combine Encoded Comparator
  }
  skpspc();
  if (cmprtr) prstrm();
  cmprtr = (cmprtr ^ revrse) & 7; //Apply reversal
  prccmp();
  DEBUG("Parsed comparator %d\n", cmprtr)
}

/* Parse Flag Operator */
void prsflg(int revrse) {
  DEBUG("Parsing Flag Operator '%c'\n", nxtchr)
  if (match('+'))      cmprtr = 0;
  else if (match('-')) cmprtr = 1;
  else                 expctd("Flag operator");
  skpchr();
  cmprtr = (cmprtr ^ revrse) & 1;  //Apply Reversal
  if (cmprtr) asmlin("BPL", cndlbl);
  else        asmlin("BMI", cndlbl);
}

/* Parse and Compile Conditional Expression     *
 * Condition = <expression> <comparator> <term> */
void prscnd(char trmntr, int revrse) {
  DEBUG("Parsing condition with REVRSE=%d\n", revrse)
  if (look('!')) {
    revrse = (revrse) ? FALSE: TRUE;
    DEBUG("Set REVRSE to %d\n", revrse)
  }
  if (!look('*')) prsxpr(0);
  if (look(':')) prsflg(revrse);  //Parse Flag Operator
  else           prscmp(revrse);  //Parse Comparison Operator
  expect(trmntr);
}