C Library for Polynomials

Poly.c

#include<stdlib.h>

typedef struct
{
   int order;
   int *coeff;
}poly;

poly clone(poly a)
{
   poly c;
   int i, n;
   c.order = a.order;
   for(i = 0; i <= c.order; i++ )
   {
      c.coeff[i] = a.coeff[i];
   }
   return c;
}
poly multiply(poly a, poly b)
{
   poly res;
   int i, o1, o2, n;
   res.order = o1 + o2;
   res.coeff = (int *)malloc(sizeof(int * (res.order + 1)));
   for(i = 0; i <= res.order; i++)
      res.coeff[i] = 0;
   for(i = 0; i <= o1; i++)
      for(j = 0; j <= o2; j++)
         res.coeff[i+j] += a.coeff[i] * b.coeff[j];
   return res;
}

poly add(poly a, poly b)
{
   int o1, o2, i;
   poly res;
   res.order = (o1>o2)?o1:o2;
   res.coeff = (int *)malloc(sizeof(int * (res.order + 1)));
   for(i = 0; i <= o1 && i <= o2; i++)
   {
      res.coeff[i] = a.coeff[i] + b.coeff[i];
   }
   while(i <= o1)
   {
      res.coeff[i] = a.coeff[i];
      i++;
   }
   while(i <= o2)
   {
      res.coeff[i] = b.coeff[i];
      i++;
   }
   res.order = i-1;
   return res;
}

poly subtract(poly a, poly b)
{
   int o1, o2, i;
   poly res;
   res.order = (o1>o2)?o1:o2;
   res.coeff = (int *)malloc(sizeof(int * (res.order + 1)));
   for(i = 0; i <= o1 && i <= o2; i++)
   {
      res.coeff[i] = a.coeff[i] - b.coeff[i];
   }
   while(i <= o1)
   {
      res.coeff[i] = a.coeff[i];
      i++;
   }
   while(i <= o2)
   {
      res.coeff[i] = - b.coeff[i];
      i++;
   }
   res.order = i-1;
   return res;
}

poly generate_node_x()
{
   poly new_node;
   new_node.order = 1;
   new_node.coeff = (int *)malloc(sizeof(int*2));
   new_node.coeff[0] = 0;
   new_node.coeff[1] = 1;
   return new_node;
}

#define AND(a,b) multiply(a,b)
#define OR(a,b) add(a,subtract(b,multiply(a,b)))