combine.c

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