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Re: Exp() function reloaded

Cross-posted to 3 groups.

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hopcode wrote:
> 
> Hi,
> here my method for the exponentianal function e^x .
> it is a mix of 2 fundamentals:
> - Taylor series running at a 10 steps for decimals -1.0 < x < +1.0
> - a couple of basic rules of the logarithms.
 
> it is ~40 lines of code (my Taylors's exp() code + main routine)
> it accepts only +numbers for now, and makes no exaustive check
> on the floats. for those and negative values i leave it to the
> reader's creativity ( being e^-x essentially 1 / e^x ).

I've code Taylors's exp(x) for both positive and negative x in C,
using -1.0 < x < +1.0,
but without making use of e^-x being essentially 1 / e^x.

/* BEGIN new.c output */

fs_expl(20.3) is 654904512.153239
fs_expl(20.3)  - 654904512.153230 is 8.583069e-006

fs_expl(-20.3) is 1.526940e-009
fs_expl(-20.3)  - 1.526940e-009   is 1.591266e-016

/* END new.c output */






/* BEGIN new.c */

#include <stdio.h>

long double fs_expl(long double x)
{
    long unsigned n, square; 
    long double b, e, old;
    
    for (square = 0; x > 1; x /= 2) {
        ++square;
    }
    while (-1 > x) {
        ++square;
        x /= 2;
    }
    e = b = n = 1;
    do {
        b /= n++;
        b *= x;
        e += b;
        b /= n++;
        b *= x;
        old = e;
        e += b;
    } while (e > old);
    while (square-- != 0) {
        e *= e;
    }
    return e;
}

int 
main(void)
{
    puts("/* BEGIN new.c output */\n");
    printf("fs_expl(20.3) is %lf\n", 
            fs_expl(20.3));
    printf("fs_expl(20.3)  - 654904512.153230 is %le\n\n", 
            fs_expl(20.3)  - 654904512.153230);


    printf("fs_expl(-20.3) is %le\n", 
            fs_expl(-20.3));
    printf("fs_expl(-20.3)  - 1.526940e-009   is %le\n\n", 
            fs_expl(-20.3)  - 1.526940e-009);

    puts("/* END new.c output */");
    return 0;
}

/* END new.c */


-- 
pete

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Exp() function reloaded hopcode <hopcode@invalid.de> - 2012-04-15 04:31 +0200
  Re: Exp() function reloaded pete <pfiland@mindspring.com> - 2012-04-15 01:26 -0400
    Re: Exp() function reloaded hopcode <hopcode@invalid.de> - 2012-04-15 12:18 +0200
      Re: Exp() function reloaded pete <pfiland@mindspring.com> - 2012-04-15 09:30 -0400
    Re: Exp() function reloaded "io_x" <a@b.c.invalid> - 2012-04-16 09:01 +0200
      Re: Exp() function reloaded "io_x" <a@b.c.invalid> - 2012-04-16 11:50 +0200
        Re: Exp() function reloaded "io_x" <a@b.c.invalid> - 2012-04-16 15:46 +0200
          Re: Exp() function reloaded "io_x" <a@b.c.invalid> - 2012-04-16 16:07 +0200
            Re: Exp() function reloaded "io_x" <a@b.c.invalid> - 2012-04-17 09:36 +0200
              Re: Exp() function reloaded phreda <pabloreda@gmail.com> - 2012-04-19 19:43 -0700
                Re: Exp() function reloaded hopcode <hopcode@invalid.de> - 2012-04-24 14:48 +0200
                Re: Exp() function reloaded phreda <pabloreda@gmail.com> - 2012-04-25 12:36 -0700
        Re: Exp() function reloaded pete <pfiland@mindspring.com> - 2012-04-16 18:12 -0400

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