/*----------------------------------------------------------------------
  File    : polymult.c
  Contents: multiply two polynomials
  Author  : Christian Borgelt
  History : 07.04.1998 file created
----------------------------------------------------------------------*/
#include <stdio.h>
#include <stdlib.h>

/*----------------------------------------------------------------------
  Preprocessor Definitions
----------------------------------------------------------------------*/
#define MAXDEGREE  64           /* maximal degree of polynomial */

/*----------------------------------------------------------------------
  Functions
----------------------------------------------------------------------*/

int polymult (int n1, double c1[], int n2, double c2[], double res[])
{                               /* --- multiply polynomials */
  int n;                        /* number of coeff. in product */
  int i, k;                     /* loop variables */

  n = n1 +n2 -1;                /* check the degree of the */
  if (n > MAXDEGREE) return -1; /* resulting polynomial */
  for (i = n; --i >= 0; )       /* clear the coefficients */
    res[i] = 0;                 /* of the resulting polynomial */
  for (i = n1; --i >= 0; )      /* traverse first polynomial */
    for (k = n2; --k >= 0; )    /* traverse second polynomial */
      res[i+k] += c1[i] *c2[k]; /* multiply coeff. and store result */
  return n;                     /* return number of coeff. in product */
}  /* polymult() */

/*--------------------------------------------------------------------*/

int main (int argc, char *argv[])
{                               /* --- main function */
  int    n1, n2, n;             /* degrees of polynomials */
  double c1 [MAXDEGREE+1];      /* coefficients of first  polynomial */
  double c2 [MAXDEGREE+1];      /* coefficients of second polynomial */
  double res[MAXDEGREE+1];      /* coefficients of product */
  FILE   *in;                   /* file to read polynomial from */

  /* --- print a usage message --- */
  if (argc != 3) {              /* if wrong number of arguments given */
    printf("usage: %s in1 in2\n", argv[0]);
    printf("multiply two polynomials\n");
    printf("The coefficients of the polynomials\n"
           "are read from the files `in1' and `in2'.\n");
    return 0;                   /* print a usage message */
  }                             /* and abort the function */

  /* --- read first polynomial --- */
  in = fopen(argv[1], "r");     /* open the file for reading */
  if (!in) {                    /* if the file cannot be opened */
    printf("%s: cannot open file `%s'\n", argv[0], argv[1]); return -1;}
  for (n1 = 0; n1 <= MAXDEGREE; n1++) {
    if (fscanf(in, "%lf", c1+n1) != 1)
      break;                    /* read the coefficients of the */
  }                             /* polynomial from the input file */
  fclose(in);                   /* close input file */
  if (n1 > MAXDEGREE) {         /* check degree of polynomial */
    printf("%s: first polynomial too large\n", argv[0]); return 1; }

  /* --- read second polynomial --- */
  in = fopen(argv[2], "r");     /* open the file for reading */
  if (!in) {                    /* if the file cannot be opened */
    printf("%s: cannot open file `%s'\n", argv[0], argv[2]); return -1;}
  for (n2 = 0; n2 <= MAXDEGREE; n2++) {
    if (fscanf(in, "%lf", c2+n2) != 1)
      break;                    /* read the coefficients of the */
  }                             /* polynomial from the input file */
  fclose(in);                   /* close input file */
  if (n2 > MAXDEGREE) {         /* check degree of polynomial */
    printf("%s: second polynomial too large\n", argv[0]); return 1; }

  /* --- compute and print product --- */
  n = polymult(n1, c1, n2, c2, res);  /* multiply polynomials */
  if (n < 0) { printf("%s: result too large\n", argv[0]); return 1; }
  for (n1 = 0; n1 < n; n1++)    /* print the coefficients */
    printf("%g\n", res[n1]);    /* of the product */
  return 0;                     /* return 'ok' */
}  /* main() */