degree.cpp

   1 #include "stdafx.h"
   2 #include "defs.h"
   3
   4 void
   5 eval_degree(void)
   6 {
   7         push(cadr(p1));
   8         eval();
   9         push(caddr(p1));
  10         eval();
  11         p1 = pop();
  12         if (p1 == symbol(NIL))
  13                 guess();
  14         else
  15                 push(p1);
  16         degree();
  17 }
  18
  19 //-----------------------------------------------------------------------------
  20 //
  21 //      Find the degree of a polynomial
  22 //
  23 //      Input:          tos-2           p(x)
  24 //
  25 //                      tos-1           x
  26 //
  27 //      Output:         Result on stack
  28 //
  29 //      Note: Finds the largest numerical power of x. Does not check for
  30 //      weirdness in p(x).
  31 //
  32 //-----------------------------------------------------------------------------
  33
  34 #define POLY p1
  35 #define X p2
  36 #define DEGREE p3
  37
  38 void
  39 degree(void)
  40 {
  41         save();
  42         X = pop();
  43         POLY = pop();
  44         DEGREE = zero;
  45         yydegree(POLY);
  46         push(DEGREE);
  47         restore();
  48 }
  49
  50 void
  51 yydegree(U *p)
  52 {
  53         if (equal(p, X)) {
  54                 if (iszero(DEGREE))
  55                         DEGREE = one;
  56         } else if (car(p) == symbol(POWER)) {
  57                 if (equal(cadr(p), X) && isnum(caddr(p)) && lessp(DEGREE, caddr(p)))
  58                         DEGREE = caddr(p);
  59          } else if (iscons(p)) {
  60                 p = cdr(p);
  61                 while (iscons(p)) {
  62                         yydegree(car(p));
  63                         p = cdr(p);
  64                 }
  65         }
  66 }