source: trunk/test/math/poly.cpp @ 1011 Tweet

//
// Lol Engine - Sample math program: chek trigonometric functions
//
// Copyright: (c) 2005-2011 Sam Hocevar <sam@hocevar.net>
//   This program is free software; you can redistribute it and/or
//   modify it under the terms of the Do What The Fuck You Want To
//   Public License, Version 2, as published by Sam Hocevar. See
//   http://sam.zoy.org/projects/COPYING.WTFPL for more details.
//

#if defined HAVE_CONFIG_H
#   include "config.h"
#endif

#include <cstdio>

#include "core.h"

using namespace lol;
using namespace std;

static float adjust(float f, int i)
{
    union { float f; uint32_t x; } u = { f };
    u.x += i;
    return u.f;
}

static void inspect(float f)
{
    union { float f; uint32_t x; } u = { f };
    printf("%08x %g  --  ", u.x, u.f);
    int i = (u.x & 0x7fffffu) | 0x800000u;
    int j = 23 - ((u.x >> 23) & 0xff) + ((1 << 7) - 1);
    if (u.f <= 0)
        i = -i;
    printf("%i / 2^%i = %g\n", i, j, (float)i / (1LLu << j));
}

static float const a0 = adjust(1.0, 0);
static float const a1 = adjust(-0.1666666666372165, 0);
static float const a2 = adjust(0.008333332748323419, 0);
static float const a3 = adjust(-0.0001984108245332497, 0);
static float const a4 = adjust(2.753619853326498e-06, 0);
static float const a5 = adjust(-2.407483949485896e-08, 0);

static float floatsin(float f)
{
    //return lol_sin(f);
//#define float double
    //static float const k = (float)real::R_2_PI;

    //f *= k;
    float f2 = f * f;
    float f4 = f2 * f2;
    //return f * (a0 + f4 * (a2 + f4 * a4) + f2 * (a1 + f4 * (a3 + f4 * a5)));
    //return f * (a0 + f2 * (a1 + f2 * (a2 + f2 * (a3 + f2 * (a4 + f2 * a5)))));
    return f * (a0 + a1 * f2 + a2 * f2 * f2 + a3 * f2 * f2 * f2 + a4 * f2 * f2 * f2 * f2 + a5 * f2 * f2 * f2 * f2 * f2);
#undef float
}

int main(void)
{
    int error[5] = { 0 };

    inspect(a0);
    inspect(a1);
    inspect(a2);
    inspect(a3);
    inspect(a4);
    inspect(a5);

    for (float f = (float)real::R_PI_2; f > 1e-30; f = adjust(f, -1))
    {
        union { float f; uint32_t x; } s1 = { sinf(f) };
        union { float f; uint32_t x; } s2 = { floatsin(f) };
        int e = abs((int)(s1.x - s2.x));
        switch (e)
        {
        case 0:
        case 1:
        case 2:
        case 3:
            error[e]++;
            break;
        default:
            if (fabs((double)s1.f - (double)s2.f) > 1e-10 * fabs(s1.f))
                printf("%16.14g: %16.14g %16.14g %08x %08x\n", f, s1.f, s2.f, s1.x, s2.x);
            error[4]++;
            break;
        }
    }

    printf("exact: %i  off by 1: %i  by 2: %i  by 3: %i  error: %i\n",
           error[0], error[1], error[2], error[3], error[4]);

    return EXIT_SUCCESS;
}