File: classic.c

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/* classic.c: Classic operations used in libquantum

   Copyright 2003, 2004 Bjoern Butscher, Hendrik Weimer

   This file is part of libquantum

   libquantum is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published
   by the Free Software Foundation; either version 3 of the License,
   or (at your option) any later version.

   libquantum is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with libquantum; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301, USA

*/

#include <math.h>

/* Calculate A^B with A and B as integers */

int
quantum_ipow(int a, int b)
{
  int i;
  int r=1;

  for(i=0; i<b ;i++)
    r*=a;

  return r;
}

/* Calculate the greatest common divisor with Euclid's algorithm */

int
quantum_gcd(int u, int v)
{
  int r;

  while(v)
    {
      r = u % v;
      u = v;
      v = r;
    }
  return u;
}

/* Fractional approximation of a decimal value */

void
quantum_frac_approx(int *a, int *b, int width)
{
  float f = (float) *a / *b;
  float g=f;
  int i, num2=0, den2=1, num1=1, den1=0, num=0, den=0;
 
  do
    {
      i = (int) (g+0.000005);
      
      g -= i-0.000005;
      g = 1.0/g;

      if (i * den1 + den2 > 1<<width)
	break;

      num = i * num1 + num2;
      den = i * den1 + den2;

      num2 = num1;
      den2 = den1;
      num1 = num;
      den1 = den;

    } while(fabs(((double) num / den) - f) > 1.0 / (2 * (1 << width)));
  
  *a = num;
  *b = den;

  return;
}

/* Calculates the number of qubits required to store N */

int
quantum_getwidth(int n)
{
  int i;
  
  for(i=1; 1<<i<n; i++);

  return i;
}

/* Calculate the inverse modulus of N and C */

int
quantum_inverse_mod(int n, int c)
{
  int i;

  for(i=1; (i*c)%n!=1; i++);

  return i;
}