kunlun/dtest/ada_test/math.c

#include "math.h"

float iot_abs(float x) 
{
    if(x<0) x=0-x;
    return x;
}

float iot_sin(float x) 
{
    const float B = 1.2732395447; 
    const float C = -0.4052847346;
    const float P = 0.2310792853;//0.225; 
    float y = B * x + C * x * iot_abs(x);
    y = P * (y * iot_abs(y) - y) + y;
    return y;
 }

float iot_cos(float x) 
{
    const float Q = 1.5707963268;
    const float PI =3.1415926536;
    x += Q; 

    if(x > PI) 
        x -= 2 * PI; 

    return( iot_sin(x));
}

float iot_sqrt(float a)
{
    double x,y;
    x=0.0;
    y=a/2;
    while(x!=y)
    {
        x=y;
        y=(x+a/x)/2;
    }
    return x;
}

float iot_pow(float a,int b)
{
    float r=a;
    if(b>0)
    {
      while(--b)
         r*=a;

    }
    else if(b<0)
    {
        while(++b)     
            r*=a;
        r=1.0/r;
    }
    else r=0;
    return r;
}


static double Sqrt(double x)
{
    if (x < 0)
        return -1;
    if (x == 0)
        return 0;
    double y = (double)iot_sqrt((double)x);

    return (y + x / y) / 2;
}

static double NegativeLog(double q)
{                           
    int p;
    double pi2 = 6.283185307179586476925286766559;
    double eps2 = 0.00000000000001; // 1e-14
    double eps1;    // 1e-28
    double r = q, s = q, n = q, q2 = q * q, q1 = q2 * q;

    eps1 = eps2 * eps2;

    for (p = 1; (n *= q1) > eps1; s += n, q1 *= q2)
        r += (p = !p) ? n : -n;

    double u = 1 - 2 * r, v = 1 + 2 * s, t = u / v;
    double a = 1, b = Sqrt(1 - t * t * t * t);

    for (; a - b > eps2; b = Sqrt(a * b), a = t)
        t = (a + b) / 2;

    return pi2 / (a + b) / v / v;
}

static double Log(double x)
{
    int k = 0;
    double ln10 = 2.30258509299404568401799145468;

    if (x <= 0)
        return -1;
    if (x == 1)
        return 0;

    for (; x > 0.1; k++)
        x /= 10;
    for (; x <= 0.01; k--)
        x *= 10;

    return k * ln10 - NegativeLog(x);
}

double Log10(double x)
{
    double ln10 = 2.30258509299404568401799145468;

    return Log(x) / ln10;
}