135 lines
1.7 KiB
C++
135 lines
1.7 KiB
C++
// get the coefficient of x^n in polynomial p(x)
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#include "stdafx.h"
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#include "defs.h"
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#define P p1
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#define X p2
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#define N p3
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void
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eval_coeff(void)
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{
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push(cadr(p1)); // 1st arg, p
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eval();
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push(caddr(p1)); // 2nd arg, x
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eval();
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push(cadddr(p1)); // 3rd arg, n
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eval();
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N = pop();
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X = pop();
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P = pop();
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if (N == symbol(NIL)) { // only 2 args?
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N = X;
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X = symbol(SYMBOL_X);
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}
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push(P); // divide p by x^n
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push(X);
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push(N);
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power();
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divide();
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push(X); // keep the constant part
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filter();
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}
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//-----------------------------------------------------------------------------
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//
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// Put polynomial coefficients on the stack
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//
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// Input: tos-2 p(x)
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//
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// tos-1 x
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//
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// Output: Returns number of coefficients on stack
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//
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// tos-n Coefficient of x^0
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//
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// tos-1 Coefficient of x^(n-1)
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//
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//-----------------------------------------------------------------------------
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int
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coeff(void)
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{
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int h, n;
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save();
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p2 = pop();
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p1 = pop();
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h = tos;
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for (;;) {
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push(p1);
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push(p2);
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push(zero);
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subst();
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eval();
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p3 = pop();
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push(p3);
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push(p1);
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push(p3);
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subtract();
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p1 = pop();
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if (equal(p1, zero)) {
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n = tos - h;
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restore();
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return n;
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}
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push(p1);
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push(p2);
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divide();
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p1 = pop();
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}
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}
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#if SELFTEST
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static char *s[] = {
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"coeff(40*x^3+30*x^2+20*x+10,3)",
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"40",
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"coeff(40*x^3+30*x^2+20*x+10,2)",
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"30",
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"coeff(40*x^3+30*x^2+20*x+10,1)",
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"20",
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"coeff(40*x^3+30*x^2+20*x+10,0)",
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"10",
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"coeff(a*t^3+b*t^2+c*t+d,t,3)",
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"a",
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"coeff(a*t^3+b*t^2+c*t+d,t,2)",
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"b",
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"coeff(a*t^3+b*t^2+c*t+d,t,1)",
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"c",
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"coeff(a*t^3+b*t^2+c*t+d,t,0)",
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"d",
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};
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void
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test_coeff(void)
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{
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test(__FILE__, s, sizeof s / sizeof (char *));
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}
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#endif
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