Fork of the espurna firmware for `mhsw` switches
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/**
* This code is available at
* http://www.mindspring.com/~pfilandr/C/fs_math/
* and it is believed to be public domain.
*/
/* BEGIN fs_math.h */
/*
** Portable freestanding code.
*/
#ifndef H_FS_MATH_H
#define H_FS_MATH_H
double fs_sqrt(double x);
double fs_log(double x);
double fs_log10(double x);
/*
** exp(x) = 1 + x + x^2/2! + x^3/3! + ...
*/
double fs_exp(double x);
double fs_modf(double value, double *iptr);
double fs_fmod(double x, double y);
double fs_pow(double x, double y);
double fs_cos(double x);
/*
** C99
*/
double fs_log2(double x);
double fs_exp2(double x);
long double fs_powl(long double x, long double y);
long double fs_sqrtl(long double x);
long double fs_logl(long double x);
long double fs_expl(long double x);
long double fs_cosl(long double x);
long double fs_fmodl(long double x, long double y);
#endif
/* END fs_math.h */
#if 0
/*
> > Anybody know where I can get some source code for a
> > reasonably fast double
> > precision square root algorithm in C.
> > I'm looking for one that is not IEEE
> > compliant as I am running on a Z/OS mainframe.
> >
> > I would love to use the standard library but
> > unfortunatly I'm using a
> > stripped down version of C that looses the the runtime library
> > (we have to write our own).
>
> long double Ssqrt(long double x)
> {
> long double a, b;
> size_t c;
size_t is a bug here.
c needs to be a signed type:
long c;
> if (x > 0) {
> c = 0;
> while (x > 4) {
> x /= 4;
> ++c;
> }
> while (1.0 / 4 > x) {
> x *= 4;
> --c;
> }
> a = x;
> b = ((4 > a) + a) / 2;
Not a bug, but should be:
b = (1 + a) / 2;
> do {
> x = b;
> b = (a / x + x) / 2;
> } while (x > b);
> if (c > 0) {
The above line is why c needs to be a signed type,
otherwise the decremented values of c, are greater than zero,
and the function won't work if the initial value of x
is less than 0.25
> while (c--) {
> x *= 2;
> }
> } else {
> while (c++) {
> x /= 2;
> }
> }
> }
> return x;
> }
>
> >
> > That algorithm was actually 4 times slower
> > then the one below, and more
> > code. It was accurate though.
> >
>
> Sorry Pete, I wasn't looking very carefully.
> When I converted your function
> to double precision it's was much quicker, the best I've seen yet.
*/
#endif