combine.c

   1 #include <polylib/polylibgmp.h>
   2 #include "combine.h"
   3
   4 /*
   5  * Vector p3 is a linear combination of two vectors (p1 and p2) such that
   6  * p3[pos] is zero. First element of each vector (p1,p2,p3) is a status
   7  * element and is not changed in p3. The value of 'pos' may be 0 however.
   8  * The parameter 'length' does not include status element one.
   9  *
  10  * This function was copied from the PolyLib source.
  11  */
  12 void Combine(Value *p1, Value *p2, Value *p3, int pos, unsigned length) {
  13
  14   Value a1, a2, gcd;
  15   Value abs_a1,abs_a2,neg_a1;
  16
  17   /* Initialize all the 'Value' variables */
  18   value_init(a1); value_init(a2); value_init(gcd);
  19   value_init(abs_a1); value_init(abs_a2); value_init(neg_a1);
  20
  21   /* a1 = p1[pos] */
  22   value_assign(a1,p1[pos]);
  23
  24   /* a2 = p2[pos] */
  25   value_assign(a2,p2[pos]);
  26
  27   /* a1_abs = |a1| */
  28   value_absolute(abs_a1,a1);
  29
  30   /* a2_abs = |a2| */
  31   value_absolute(abs_a2,a2);
  32
  33   /* gcd  = Gcd(abs(a1), abs(a2)) */
  34   Gcd(abs_a1,abs_a2,&gcd);
  35
  36   /* a1 = a1/gcd */
  37   value_division (a1,a1,gcd);
  38
  39   /* a2 = a2/gcd */
  40   value_division (a2,a2,gcd);
  41
  42   /* neg_a1 = -(a1) */
  43   value_oppose(neg_a1,a1);
  44
  45   Vector_Combine(p1+1,p2+1,p3+1,a2,neg_a1,length);
  46   Vector_Normalize(p3+1,length);
  47
  48   /* Clear all the 'Value' variables */
  49   value_clear(a1); value_clear(a2); value_clear(gcd);
  50   value_clear(abs_a1); value_clear(abs_a2); value_clear(neg_a1);
  51
  52   return;
  53 } /* Combine */
  54