www.pudn.com > 文件恢复及修补 C 语言源程序.zip > LOG.C

 
/*********************************************************** 
 *               The TULSA IBM C BOARD                     * 
 *                   918-664-8737                          * 
 *             300/1200 XMODEM, 24 Hours                   * 
 **********************************************************/ 
 
 
#include "math.h" 
#include "errno.h" 
 
double log10(x) 
double x; 
{ 
        return log(x)*0.43429448190325182765; 
} 
 
#define A0 -0.64124943423745581147e+2 
#define A1 +0.16383943563021534222e+2 
#define A2 -0.78956112887491257267e+0 
#define A(w) ((A2*w A1)*w A0) 
 
#define B0 -0.76949932108494879777e+3 
#define B1 +0.31203222091924532844e+3 
#define B2 -0.35667977739034646171e+2 
#define B(w) (((w B2)*w B1)*w B0) 
 
#define C0 0.70710678118654752440 
#define C1 0.693359375 
#define C2 -2.121944400546905827679e-4 
 
double log(x) 
double x; 
{ 
        double Rz, f, z, w, znum, zden, xn; 
        int n; 
        extern int errno; 
 
        if (x <= 0.0) { 
                errno = EDOM; 
                return -HUGE; 
        } 
        f = frexp(x, &n); 
        if (f > C0) { 
                znum = (znum = f-0.5) - 0.5; /* the assignment prevents const. eval */ 
                zden = f*0.5 + 0.5; 
        } else { 
                --n; 
                znum = f - 0.5; 
                zden = znum*0.5 + 0.5; 
        } 
        z = znum/zden; 
        w = z*z; 
/* the lines below are split up to allow expansion of A(w) and B(w) */ 
        Rz = z + z * (w * 
                         A(w) 
                        /B(w)); 
        xn = n; 
        return (xn*C2 + Rz) + xn*C1; 
}