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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
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