/***********************************************************************
 *
 *		EVAL.C
 *		Expression Evaluator for 68000 Assembler
 *
 *    Function: eval()
 *		Evaluates a constant expression. The p argument points
 *		to the string to be evaluated, and the function returns
 *		a pointer to the first character beyond the end of the
 *		expression. The value of the expression and an error
 *		code are returned via output arguments. The function
 *		handles errors according to the following table:
 *
 *				   Pass1        Pass1   Pass2         Pass2
 *		Condition          Error        *refPtr Error         *refPtr
 *		----------------   ----------   -----   -----------   -----
 *		Undefined symbol   INCOMPLETE   FALSE   UNDEFINED     FALSE
 *		Division by zero   INCOMPLETE   FALSE   DIV_BY_ZERO   FALSE
 *		Syntax error       SYNTAX	  --      SYNTAX        --
 * 		Constant error     x_TOO_BIG    T/F     x_TOO_BIG     T/F
 *		No error           OK           T/F     OK            T/F
 *
 *		The char pointed to by refPtr is set to true if all the
 *		symbols encountered in the expression are backwards
 *		references or FALSE if at least one symbol is a forward
 *		reference. 
 *
 *	 Usage:	char *eval(p, valuePtr, refPtr, errorPtr)
 *		char *p;
 *		int  *valuePtr;
 *		char *refPtr;
 *		int  *errorPtr;
 *
 *	Errors: ASCII_TOO_BIG
 *		DIV_BY_ZERO
 *		INCOMPLETE
 *		NUMBER_TOO_BIG
 *		REG_LIST_SPEC
 *		SYNTAX
 *		UNDEFINED
 *
 *      Author: Paul McKee
 *		ECE492    North Carolina State University
 *
 *        Date:	9/24/86
 *
 *    Modified: Charles Kelly
 *              Monroe County Community College
 *              http://www.monroeccc.edu/ckelly
 ************************************************************************/


#include <stdio.h>
#include <ctype.h>
#include "asm.h"

extern bool pass2;
extern int loc;
extern char buffer[256];  //ck used to form messages for display in windows
extern char numBuf[20];

// Largest number that can be represented in an unsigned int
//	- MACHINE DEPENDENT
//ck #define INTLIMIT 0xFFFF
//ck #define LONGLIMIT 0xFFFFFFFF
const unsigned int LONGLIMIT = 0xFFFFFFFF;         //ck

#define STACKMAX 5

char *eval(char	*p, int *valuePtr, bool *refPtr, int *errorPtr)
{
  int	valStack[STACKMAX];
  char	opStack[STACKMAX-1];
  int	valPtr = 0;
  int	opPtr = 0;
  int	t;
  int	prec;
  int	i;
  bool	evaluate, backRef;
  int	status;

  try {
    // Assume that the expression is to be evaluated,
    //   at least until an undefined symbol is found
    evaluate = true;
    // Assume initially that all symbols are backwards references
    *refPtr = true;
    // Loop until terminator character is found (loop is exited via return)
    while (true) {
      /************************************************
       *						                      *
       *		        EXPECT AN OPERAND		      *
       *						                      *
       ************************************************/
      // Use evalNumber to read in a number or symbol
      status = OK;
      p = evalNumber(p, &t, &backRef, &status);
      NEWERROR(*errorPtr, status);
      if (!backRef && status > ERRORN) {        // || status == INCOMPLETE)) {
        // Stop evaluating the expression
        *refPtr = false;
        return p;                       // ck 4-16-2002
      }
      else if (*errorPtr > SEVERE)
        // Pass any other error to the caller
        return NULL;
      else {
        // If OK or WARNING, push the value on the stack
        if (evaluate)
          valStack[valPtr++] = t;
        // Set *refPtr to reflect the symbol just parsed
        *refPtr = (char) (*refPtr && backRef);
      }

      /************************************************
       *						                      *
       *	    	EXPECT AN OPERATOR	              *
       *						                      *
       ************************************************/
      // Handle the >> and << operators
      if (*p == '>' || *p == '<') {
        p++;
        if (*p != *(p-1)) {
          NEWERROR(*errorPtr, SYNTAX);
          return NULL;
        }
      }
      prec = precedence(*p);
      // Do all stacked operations that are of higher
      //     precedence than the operator just examined.
      while (opPtr && evaluate && (prec <= precedence(opStack[opPtr-1]))) {
        // Pop operands and operator and do the operation
        t = valStack[--valPtr];
        i = valStack[--valPtr];
        status = doOp(i, t, opStack[--opPtr], &t);
        if (status != OK) {
          // Report error from doOp
          if (pass2) {
            NEWERROR(*errorPtr, status);
          }
          else
            NEWERROR(*errorPtr, INCOMPLETE);
          evaluate = false;
          *refPtr = false;
        }
        else
          // Otherwise push result on the stack
          valStack[valPtr++] = t;
      }
      if (prec) {
        if (evaluate)
          // If operator is valid, push it on the stack
          opStack[opPtr++] = *p;
        p++;
      }
      else if (*p==',' || *p=='(' || *p==')' || !(*p) || isspace(*p) || *p=='.' || *p=='{' || *p==':' || *p=='}') {
        // If the character terminates the expression,
        //     then return the various results needed.
        if (evaluate)
          *valuePtr = valStack[--valPtr];
        else
          *valuePtr = 0;

        return p;
      } else {
        // Otherwise report the syntax error
        NEWERROR(*errorPtr,  SYNTAX);
        return NULL;
      }
    }
  }
  catch( ... ) {
    NEWERROR(*errorPtr, EXCEPTION);
    sprintf(buffer, "ERROR: An exception occurred in routine 'eval'. \n");
    return NULL;
  }

  //return NORMAL;
}

//----------------------------------------------------------
// return the value of the operand at *p in numberPtr.
// refPtr set true if valid backwards reference.

char *evalNumber(char *p, int *numberPtr, bool *refPtr, int *errorPtr)
{
  int	status;
  int	base;
  int	x;
  char	name[SIGCHARS+1];
  symbolDef *symbol;            //ck , *lookup();
  int	i;
  bool	endFlag;

  try {

  *refPtr = true;

  //ck   * is current address
  if (*p == '*') {
    *numberPtr = loc;
    return ++p;
  }
  else if (*p == '-') {
    /* Evaluate unary minus operator recursively */
    p = evalNumber(++p, &x, refPtr, errorPtr);
    *numberPtr = -x;
    return p;
  }
  else if (*p == '~') {
    /* Evaluate one's complement operator recursively */
    p = evalNumber(++p, &x, refPtr, errorPtr);
    *numberPtr = ~x;
    return p;
  }
  else if (*p == '(') {
    /* Evaluate parenthesized expressions recursively */
    p = eval(++p, &x, refPtr, errorPtr);
    if (*errorPtr > SEVERE)
      return NULL;
    else if (*p != ')') {
      NEWERROR(*errorPtr, SYNTAX);
      return NULL;
    } else {
      *numberPtr = x;
      return ++p;
    }
  }
  else if (*p == '$' && isxdigit(*(p+1))) {
    /* Convert hex digits until another character is
       found. (At least one hex digit is present.) */
    x = 0;
    while (isxdigit(*++p)) {
      if ((unsigned int)x > (unsigned int)LONGLIMIT/16)
	NEWERROR(*errorPtr, NUMBER_TOO_BIG);
      if (*p > '9')
	x = 16 * x + (*p - 'A' + 10);
      else
	x = 16 * x + (*p - '0');
    }
    *numberPtr = x;
    return p;
  }
  else if (*p == '%' || *p == '@' || isdigit(*p)) {
    /* Convert digits in the appropriate base (binary,
       octal, or decimal) until an invalid digit is found. */
    if (*p == '%') {
      base = 2;
      p++;
    }
    else if (*p == '@') {
      base = 8;
      p++;
    }
    else
      base = 10;
    /* Check that at least one digit is present */
    if (*p < '0' || *p >= '0' + base) {
      NEWERROR(*errorPtr, SYNTAX);
      return NULL;
    }
    x = 0;
    /* Convert the digits into an integer */
    while (*p >= '0' && *p < '0' + base) {
      if ((unsigned int)x > ((unsigned int)(LONGLIMIT - (*p - '0')) / base)) {
	NEWERROR(*errorPtr, NUMBER_TOO_BIG);
      }
      x = (int) ( (int) ((int) base * x) + (int) (*p - '0') );
      p++;
    }
    *numberPtr = x;
    return p;
  }
  else if (*p == '\'') {        // if start of string literal
    endFlag = false;
    i = 0;
    x = 0;
    p++;
    while (!endFlag && *p) {
      if (*p == '\'')           // if '
	if (*(p+1) == '\'') {   // if ''
	  x = (x << 8) + *p;
	  i++;
	  p++;
	}
	else                    // ending ' found
	  endFlag = true;       // end of string literal
      else {
	x = (x << 8) + *p;
	i++;
      }
      p++;
    }
    if (i == 0 || *p == '\0') { // if no operand or unexpected end of string
      NEWERROR(*errorPtr, SYNTAX);
      return NULL;
    }
    else if (i == 3)
      x = x << 8;
    else if (i > 4)
      NEWERROR(*errorPtr, ASCII_TOO_BIG);
    *numberPtr = x;
    return p;
  }
  else if (isalpha(*p) || *p == '.' || *p == '_') {  // *ck 12-8-2005
    /* Determine the value of a symbol */
    i = 0;
    /* Collect characters of the symbol's name
       (only SIGCHARS characters are significant) */
    do {
      if (i < SIGCHARS)
	name[i++] = *p;
      p++;
      //} while (isalnum(*p) || *p == '_' || *p == '$' || *p == '.'); // *ck 12-8-2005 so labels may have dots
    } while (isalnum(*p) || *p == '_' || *p == '$'); // *ck 2-22-2007 operand.L caused error (no dots in labels)
    name[i] = '\0';
    /* Look up the name in the symbol table, resulting
       in a pointer to the symbol table entry */
    status = OK;
    symbol = lookup(name, false, &status);

    if (status == OK)
      /* If symbol was found, and it's not a register
         list symbol, then return its value */
      if (!(symbol->flags & REG_LIST_SYM)) {
	*numberPtr = symbol->value;

	if (pass2)
	  *refPtr = (symbol->flags & BACKREF);
      } else {
	/* If it is a register list symbol, return error */
	*numberPtr = 0;
	NEWERROR(*errorPtr, REG_LIST_SPEC);
      }
    else {
      /* Otherwise return an error */
      if (pass2) {
        if( (strncmp(name, ".0", 2)) == 0) {
          NEWERROR(*errorPtr, ENDI_EXPECTED);
        } else if( (strncmp(name, ".1", 2)) == 0) {
          NEWERROR(*errorPtr, ENDW_EXPECTED);
        } else if( (strncmp(name, ".2", 2)) == 0) {
          NEWERROR(*errorPtr, ENDF_EXPECTED);
        } else if( (strncmp(name, ".3", 2)) == 0) {
          NEWERROR(*errorPtr, REPEAT_EXPECTED);
        } else {
          NEWERROR(*errorPtr, UNDEFINED);
        }
      }
      else
        NEWERROR(*errorPtr, INCOMPLETE);
      *refPtr = false;
    }

    return p;
  } else {
    /* Otherwise, the character was not a valid operand */
    NEWERROR(*errorPtr, SYNTAX);
    return NULL;
  }
  }
  catch( ... ) {
    NEWERROR(*errorPtr, EXCEPTION);
    sprintf(buffer, "ERROR: An exception occurred in routine 'evalNumber'. \n");
    return NULL;
  }

  //ck return NORMAL;
}



int precedence(char op)
{
  /* Compute the precedence of an operator. Higher numbers indicate
     higher precedence, e.g., precedence('*') > precedence('+').
     Any character which is not a binary operator will be assigned
     a precedence of zero. */
  switch (op) {
    case '+' :
    case '-' : return 1;
    case '&' :                  // AND
    case '!' :                  // OR
    case '|' :                  // OR
    case '^' : return 3;        // XOR
    case '>' :
    case '<' : return 4;
    case '*' :
    case '/' :
    case '\\': return 2;
    default  : return 0;
  }

  //ck return NORMAL;
}



int doOp(int val1, int val2, char op, int *result)
{

  /* Performs the operation of the operator on the two operands.
     Returns OK or DIV_BY_ZERO. */

  switch (op) {
    case '+' : *result = val1 + val2;  return OK;
    case '-' : *result = val1 - val2;  return OK;
    case '&' : *result = val1 & val2;  return OK;
    case '!' : case '|': *result = val1 | val2;  return OK;
    case '^' : *result = val1 ^ val2;  return OK;       // ck 12-11-2006
    case '>' : *result = (unsigned) val1 >> val2; return OK;
    case '<' : *result = val1 << val2; return OK;
    case '*' : *result = val1 * val2;  return OK;
    case '/' :
      if (val2 != 0) {
	*result = val1 / val2;
	return OK;
      }
      else
	return DIV_BY_ZERO;
    case '\\':
      if (val2 != 0) {
	*result = val1 % val2;
	return OK;
      }
      else
	return DIV_BY_ZERO;
  }
  return INV_OPERATOR;
}



