/*
 Author: Jose Romeo Vela        Date: March 24, 2002
 email: jrvela@aristasol.com
 http://www.aristasol.com/

 This software is licensed under GNU's GPL. For details see http://www.gnu.org/ 

 Copyright (c) 2002, Jose Romeo Vela

==============================================================================
Modifications:
   4/9/2002 jrv
      Check for NULL file handle on IN and OUT operations.

   4/13/2002 jrv2
      Cleaned the code in the case statement in function cinc_exec.

   4/15/2002 jrv3
      Fix a bug introduced by jrv2 in cardiac_SUB

*/


#include <stdlib.h>
#include "config.h"


int cinc_fetch(struct cardiac_s * cardiac)
{
  int rc = 0;
  
  
  if (cardiac->ram[cardiac->pc] > 0) {
    /* fetch the opcode */
    cardiac->opcode=cardiac->ram[cardiac->pc]/100;

    /* fetch the address or operand */
    cardiac->address=cardiac->ram[cardiac->pc] - cardiac->opcode*100;
    
    /* increment the program counter */
    cardiac->pc++;
  } else {
    /* negative instructions are invalid */
    rc = 1;
  }
  
  return(rc);
}


int cinc_exec(struct cardiac_s * cardiac)
{
  int rc = 0;
  int exit_code = 0;

  /* execute the instruction indicated in the opcode */

  switch (cardiac->opcode) {
  case 0:
    exit_code = cardiac_INP(cardiac);
    break;
  case 1:
    exit_code = cardiac_CLA(cardiac);
    break;
  case 2:
    exit_code = cardiac_ADD(cardiac);
    break;
  case 3:
    exit_code = cardiac_TAC(cardiac);
    break;
  case 4:
    exit_code = cardiac_SFT(cardiac);
    break;
  case 5:
    exit_code = cardiac_OUT(cardiac);
    break;
  case 6:
    exit_code = cardiac_STO(cardiac);
    break;
  case 7:
    exit_code = cardiac_SUB(cardiac);
    break;
  case 8:
    exit_code = cardiac_JMP(cardiac);
    break;
  case 9:
    exit_code = cardiac_HRS(cardiac);
    break;
  }  
  
  if (exit_code)
    {
      rc = 100+cardiac->opcode*10+exit_code;
      cardiac->running = FALSE;
    }

  return(rc);
}

void setsign(struct cardiac_s * cardiac)
{ /* separate the sign from the absolute value of the accumulator */
  if (cardiac->ac<0) {
    cardiac->ac_sign = -1;
    cardiac->ac = abs(cardiac->ac);
  } else {
    cardiac->ac_sign = 1;
  }
}

/* 
Each CARDIAC instruction is implemented with a separate function. These
functions are named cardiac_ followded by the abbriviated instruction
name as per CARDIAC's documentation. Here is a summary of the instructions

code   abbr  Meaning
 0     INP   Input
 1     CLA   Clear and Add
 2     ADD   Add
 3     TAC   Test Accumulator Contents
 4     SFT   Shift
 5     OUT   Output
 6     STO   Store
 7     SUB   Subtract
 8     JMP   Jump
 9     HRS   Halt and Reset
 
*/

int cardiac_INP(struct cardiac_s * cardiac)
{
  int rc = 0;
  int scan_rc;
  int cont;

  if (cardiac->IN == NULL) {
    /* No IN file specified in command line option */
    rc = 3;
    return(rc);
  }
  
  if ( cardiac-> IN == stdin) {
    fprintf(tty,"%s",CINCPROMPT);
  };

  if ( (scan_rc = fscanf(cardiac->IN,"%4d",&cont)) > 0) {
    cardiac->ram[cardiac->address]=cont;
  } else {
    /* IN file could not be opened */
    rc = 2;
  }
  return(rc);
}

int cardiac_CLA(struct cardiac_s * cardiac)
{ /* clear AC and add */
  int rc = 0;
  
  cardiac->ac = cardiac->ram[cardiac->address];

  setsign(cardiac);

  return(rc);
}

int cardiac_ADD(struct cardiac_s * cardiac)
{
  int rc = 0;
  
  cardiac->ac = cardiac->ram[cardiac->address] + cardiac->ac_sign*cardiac->ac;

  setsign(cardiac);

  /* Truncate the AC to 4 digits */
  cardiac->ac = itrunc(cardiac->ac,4);

  
  return(rc);
}

int cardiac_TAC(struct cardiac_s * cardiac)
{
  int rc = 0;

  if (cardiac->ac_sign < 0) cardiac->pc = cardiac->address;

  return(rc);
}

int cardiac_SFT(struct cardiac_s * cardiac)
{
  int rc = 0;
  
  int left;  
  int right;
  

  /* left is how many digits to shift left */
  left = cardiac->address/10;

  /* right is how many digits to shift right */
  right = cardiac->address - left*10;

  /* shift left */
  cardiac->ac = cardiac->ac*ipow(10,left);

  /* Truncate the AC to 4 digits */
  cardiac->ac = itrunc(cardiac->ac,4);


  /* shift right */
  cardiac->ac = cardiac->ac/ipow(10,right);

  return(rc);
}

int cardiac_OUT(struct cardiac_s * cardiac)
{
  int rc = 0;

  if (cardiac->OUT == NULL) {
    rc = 3;
    return(rc);
  }

  
  fprintf(cardiac->OUT,"% 04d\n",cardiac->ram[cardiac->address]);

  return(rc);
}

int cardiac_STO(struct cardiac_s * cardiac)
{
  int rc = 0;
  
  if (cardiac->address != 0) {
    cardiac->ram[cardiac->address] = (cardiac->ac - (cardiac->ac/1000)*1000) * cardiac->ac_sign;
    if (cardiac->address == (MAXRAM-1)) {
      /* last memory cell allways has opcode 8 (JMP) */
      cardiac->ram[cardiac->address] = abs(cardiac->ram[cardiac->address]);
      cardiac->ram[cardiac->address] = 
	cardiac->ram[cardiac->address] - (cardiac->ram[cardiac->address]/100)*100+800;

    }
  }
  return(rc);
}

int cardiac_SUB(struct cardiac_s * cardiac)
{
  int rc = 0;

  cardiac->ac = cardiac->ac_sign*cardiac->ac - cardiac->ram[cardiac->address];

  setsign(cardiac);

  /* Truncate the AC to 4 digits */
  cardiac->ac = itrunc(cardiac->ac,4);



  return(rc);
}

int cardiac_JMP(struct cardiac_s * cardiac)
{
  int rc = 0;
  cardiac->ram[MAXRAM-1] = 800+cardiac->pc;
  cardiac->pc = cardiac->address;

  return(rc);
}

int cardiac_HRS(struct cardiac_s * cardiac)
{
  int rc = 0;

  
  cardiac->pc = cardiac->address;

  /* stop cardiac */
  cardiac->running = 0;
  
  return(rc);
}

int ipow(int a, int b)
{ /* a to the power of b */
  int pow;
  int i;
  
  pow = 1;
  for (i = 1; i <= b; i++)
    pow *= a;

  return(pow);
}

int itrunc(int a, int b)
{ /* truncate a to b digits.    */
  int r;
  int max;
  
  max = ipow(10,b);

  if (a >= max) {
     r = a - (a/max)*(max);  
  } else {
    r = a;
  }
  return(r);

}