#include "math_libm.h"
#include "math_private.h"

Include dependency graph for e_log.c:

Functions
double attribute_hidden	__ieee754_log (double x)

Variables
static const double	ln2_hi = 6.93147180369123816490e-01
static const double	ln2_lo = 1.90821492927058770002e-10
static const double	two54 = 1.80143985094819840000e+16
static const double	Lg1 = 6.666666666666735130e-01
static const double	Lg2 = 3.999999999940941908e-01
static const double	Lg3 = 2.857142874366239149e-01
static const double	Lg4 = 2.222219843214978396e-01
static const double	Lg5 = 1.818357216161805012e-01
static const double	Lg6 = 1.531383769920937332e-01
static const double	Lg7 = 1.479819860511658591e-01
static const double	zero = 0.0

Function Documentation

double attribute_hidden __ieee754_log ( double x )

Definition at line 85 of file e_log.c.

References EXTRACT_WORDS, GET_HIGH_WORD, i, j, k, Lg1, Lg2, Lg3, Lg4, Lg5, Lg6, Lg7, ln2_hi, ln2_lo, SET_HIGH_WORD, two54, and zero.

{
        double hfsq,f,s,z,R,w,t1,t2,dk;
        int32_t k,hx,i,j;
        u_int32_t lx;
        EXTRACT_WORDS(hx,lx,x);
        k=0;
        if (hx < 0x00100000) {                  /* x < 2**-1022  */
            if (((hx&0x7fffffff)|lx)==0)
                return -two54/zero;             /* log(+-0)=-inf */
            if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
            k -= 54; x *= two54; /* subnormal number, scale up x */
            GET_HIGH_WORD(hx,x);
        }
        if (hx >= 0x7ff00000) return x+x;
        k += (hx>>20)-1023;
        hx &= 0x000fffff;
        i = (hx+0x95f64)&0x100000;
        SET_HIGH_WORD(x,hx|(i^0x3ff00000));     /* normalize x or x/2 */
        k += (i>>20);
        f = x-1.0;
        if((0x000fffff&(2+hx))<3) {     /* |f| < 2**-20 */
            if(f==zero) {if(k==0) return zero;  else {dk=(double)k;
                                 return dk*ln2_hi+dk*ln2_lo;}
            }
            R = f*f*(0.5-0.33333333333333333*f);
            if(k==0) return f-R; else {dk=(double)k;
                     return dk*ln2_hi-((R-dk*ln2_lo)-f);}
        }
        s = f/(2.0+f);
        dk = (double)k;
        z = s*s;
        i = hx-0x6147a;
        w = z*z;
        j = 0x6b851-hx;
        t1= w*(Lg2+w*(Lg4+w*Lg6));
        t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
        i |= j;
        R = t2+t1;
        if(i>0) {
            hfsq=0.5*f*f;
            if(k==0) return f-(hfsq-s*(hfsq+R)); else
                     return dk*ln2_hi-((hfsq-(s*(hfsq+R)+dk*ln2_lo))-f);
        } else {
            if(k==0) return f-s*(f-R); else
                     return dk*ln2_hi-((s*(f-R)-dk*ln2_lo)-f);
        }
}