/*
 * File:   dclxvi-20130329/scalar.c
 * Author: Ruben Niederhagen, Peter Schwabe
 * Public Domain
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "scalar.h"

void scalar_setrandom(scalar_t rop, const scalar_t bound)
{
  int i;
  FILE *urand = fopen("/dev/urandom", "r");
  if (urand == NULL)
  {
    fprintf(stderr, "Could not open device file /dev/urandom");
    exit(1);
  }
  do
  {
    for(i=0;i<32;i++) 
      i[(unsigned char*)rop] = fgetc(urand);
  }
  while(!scalar_lt_vartime(rop,bound));
  fclose(urand);
}

void scalar_set_lluarray(scalar_t rop, unsigned long long v[4])
{
  int i;
  for(i=0;i<4;i++) rop[i] = v[i];
}

int scalar_getbit(const scalar_t s, unsigned int pos)
{
  assert(pos < 256);
  return (s[pos >> 6] >> (pos & 0x3f)) & 1;
}

// Returns the position of the most significant set bit
int scalar_scanb(const scalar_t s)
{
  int i;
  unsigned int pos = 0;
  for(i=255;i>0;i--)
    if(scalar_getbit(s,i) && pos == 0) pos = i;
  return pos;
}

int scalar_iszero_vartime(const scalar_t s)
{
  return ((s[0] | s[1] | s[2] | s[3]) == 0);
}

void scalar_window4(signed char r[65], const scalar_t s)
{
  char carry;
  int i;
  for(i=0;i<16;i++)
    r[i] = (s[0] >> (4*i)) & 15;
  for(i=0;i<16;i++)
    r[i+16] = (s[1] >> (4*i)) & 15;
  for(i=0;i<16;i++)
    r[i+32] = (s[2] >> (4*i)) & 15;
  for(i=0;i<16;i++)
    r[i+48] = (s[3] >> (4*i)) & 15;

  /* Making it signed */
  carry = 0;
  for(i=0;i<64;i++)
  {
    r[i] += carry;
    r[i+1] += r[i] >> 4;
    r[i] &= 15;
    carry = r[i] >> 3;
    r[i] -= carry << 4;
  }
  r[64] = carry;
}

// Returns 1 if a < b, 0 otherwise
int scalar_lt_vartime(const scalar_t a, const scalar_t b)
{
  if(a[3] < b[3]) return 1;
  if(a[3] > b[3]) return 0;
  if(a[2] < b[2]) return 1;
  if(a[2] > b[2]) return 0;
  if(a[1] < b[1]) return 1;
  if(a[1] > b[1]) return 0;
  if(a[0] < b[0]) return 1;
  if(a[0] > b[0]) return 0;
  return 0;
}

void scalar_print(FILE *fh, const scalar_t t)
{
  int i;
  for(i=3;i>=0;i--)
    fprintf(fh, "%llx", t[i]);
}