#include <stdio.h>
#include <math.h>
#include "hamming.h"

//is there a one at bit position "position" of "value"?
int isOneAt(int position,  int value) {
  //position count starts at 1, not 0
  return ((value >> position-1) & 1);
    }

//returns the value of the bit at position "position" of "value"
int getBitVal(int position, int value) {
  //position count starts at 1, not 0
  return ((isOneAt(position,value)) ? 1 : 0);
}

//set position "position" of "value" to "bit"
int setBitVal(int position, int value, int bit) {
  return ((bit>=1) ? (value | (1<<(position-1))) : (value & ~(1<<(position-1))));
}

//formatted output of "len"-bit representation of an integer "n"
int printBits(unsigned n,unsigned len) {
  if (len == 1) 
    printf("%u",n);
  else {
    printBits(n>>1,len-1);
    printf("%u",n&1);
    if ((len%8) == 0) printf(" ");
  }
}

#define y(b) 32-(b)
#define x(b) 32-5-(b)

unsigned encode(unsigned x) {

  int p[5];
  int i,j;

  int y=0;

  for (i=0;i<5;i++) p[i]=0;

  
  //map bits of x to bits of y, section by section, per T.1, assn #9 handout
  y = setBitVal(y(3),y,getBitVal(x(1),x));
  for (i=5;i<=7;i++) y = setBitVal(y(i),y,getBitVal(x(i-3),x));
  for (i=9;i<=15;i++) y = setBitVal(y(i),y,getBitVal(x(i-4),x));
  for (i=17;i<=31;i++) y = setBitVal(y(i),y,getBitVal(x(i-5),x));

  for (i=1;i<=31;i++)
    for (j=1;j<=5;j++)
    //if this i has a 1 in position j (i.e., i belongs to C_j)
      if (isOneAt(j,i))
    //then if the plaintext x has a 1 in position i toggle parity of C_j
	if (isOneAt(y(i),y)) p[j-1] = 1-p[j-1];


  //map parity bits onto y, per T.1, assn #9 handout
  for (i=0;i<=4;i++) y=setBitVal(y(pow(2,i)),y,p[i]);

     return y;
  
  }