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