coeff.cpp

   1 // get the coefficient of x^n in polynomial p(x)
   2
   3 #include "stdafx.h"
   4 #include "defs.h"
   5
   6 #define P p1
   7 #define X p2
   8 #define N p3
   9
  10 void
  11 eval_coeff(void)
  12 {
  13         push(cadr(p1));                 // 1st arg, p
  14         eval();
  15
  16         push(caddr(p1));                // 2nd arg, x
  17         eval();
  18
  19         push(cadddr(p1));               // 3rd arg, n
  20         eval();
  21
  22         N = pop();
  23         X = pop();
  24         P = pop();
  25
  26         if (N == symbol(NIL)) {         // only 2 args?
  27                 N = X;
  28                 X = symbol(SYMBOL_X);
  29         }
  30
  31         push(P);                        // divide p by x^n
  32         push(X);
  33         push(N);
  34         power();
  35         divide();
  36
  37         push(X);                        // keep the constant part
  38         filter();
  39 }
  40
  41 //-----------------------------------------------------------------------------
  42 //
  43 //      Put polynomial coefficients on the stack
  44 //
  45 //      Input:          tos-2           p(x)
  46 //
  47 //                      tos-1           x
  48 //
  49 //      Output:         Returns number of coefficients on stack
  50 //
  51 //                      tos-n           Coefficient of x^0
  52 //
  53 //                      tos-1           Coefficient of x^(n-1)
  54 //
  55 //-----------------------------------------------------------------------------
  56
  57 int
  58 coeff(void)
  59 {
  60         int h, n;
  61
  62         save();
  63
  64         p2 = pop();
  65         p1 = pop();
  66
  67         h = tos;
  68
  69         for (;;) {
  70
  71                 push(p1);
  72                 push(p2);
  73                 push(zero);
  74                 subst();
  75                 eval();
  76
  77                 p3 = pop();
  78                 push(p3);
  79
  80                 push(p1);
  81                 push(p3);
  82                 subtract();
  83
  84                 p1 = pop();
  85
  86                 if (equal(p1, zero)) {
  87                         n = tos - h;
  88                         restore();
  89                         return n;
  90                 }
  91
  92                 push(p1);
  93                 push(p2);
  94                 divide();
  95                 p1 = pop();
  96         }
  97 }