Trailing-Edge
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PDP-10 Archives
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SRI_NIC_PERM_FS_1_19910112
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kcc-5/lib/math/poly.c
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/*
* +++ NAME +++
*
* POLY Double precision polynomial evaluation
*
* +++ INDEX +++
*
* POLY
* machine independent routines
* math libraries
*
* +++ DESCRIPTION +++
*
* Evaluates a polynomial and returns double precision
* result. Is passed a the order of the polynomial,
* a pointer to an array of double precision polynomial
* coefficients (in ascending order), and the independent
* variable.
*
* +++ USAGE +++
*
* double _poly(order,coeffs,x)
* int order;
* double *coeffs;
* double x;
*
* +++ PROGRAMMER +++
*
* Fred Fish
* Goodyear Aerospace Corp, Arizona Div.
* (602) 932-7000 work
* (602) 894-6881 home
*
* +++ INTERNALS +++
*
* Evalates the polynomial using recursion and the form:
*
* P(x) = P0 + x(P1 + x(P2 +...x(Pn)))
*
* ---
*/
#include "math.h"
double _poly(order,coeffs,x)
register int order;
register double *coeffs;
double x;
{
double curr_coeff;
if (order <= 0)
return *coeffs;
else {
curr_coeff = *coeffs++;
return curr_coeff + x * _poly(--order, coeffs, x);
}
}
/*
* NOTE: If you try to be clever and eliminate the curr_coeff
* variable in the return line, by substituting
* *coeffs++, disaster may strike if your compiler
* does not guarantee left-to-right evaluation.
*/