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glibc  2.9
Functions | Variables
e_log2.c File Reference
#include "math.h"
#include "math_private.h"

Go to the source code of this file.

Functions

double __ieee754_log2 (double x)

Variables

static double ln2 = 0.69314718055994530942
static double two54 = 1.80143985094819840000e+16
static double Lg1 = 6.666666666666735130e-01
static double Lg2 = 3.999999999940941908e-01
static double Lg3 = 2.857142874366239149e-01
static double Lg4 = 2.222219843214978396e-01
static double Lg5 = 1.818357216161805012e-01
static double Lg6 = 1.531383769920937332e-01
static double Lg7 = 1.479819860511658591e-01
static double zero = 0.0

Function Documentation

double __ieee754_log2 ( double  x)

Definition at line 84 of file e_log2.c.

{
       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/(x-x);        /* log(+-0)=-inf */
           if (hx<0) return (x-x)/(x-x);  /* 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);
       dk = (double) k;
       f = x-1.0;
       if((0x000fffff&(2+hx))<3) { /* |f| < 2**-20 */
           if(f==zero) return dk;
           R = f*f*(0.5-0.33333333333333333*f);
           return dk-(R-f)/ln2;
       }
       s = f/(2.0+f);
       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;
           return dk-((hfsq-(s*(hfsq+R)))-f)/ln2;
       } else {
           return dk-((s*(f-R))-f)/ln2;
       }
}

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Variable Documentation

double Lg1 = 6.666666666666735130e-01 [static]

Definition at line 67 of file e_log2.c.

double Lg2 = 3.999999999940941908e-01 [static]

Definition at line 68 of file e_log2.c.

double Lg3 = 2.857142874366239149e-01 [static]

Definition at line 69 of file e_log2.c.

double Lg4 = 2.222219843214978396e-01 [static]

Definition at line 70 of file e_log2.c.

double Lg5 = 1.818357216161805012e-01 [static]

Definition at line 71 of file e_log2.c.

double Lg6 = 1.531383769920937332e-01 [static]

Definition at line 72 of file e_log2.c.

double Lg7 = 1.479819860511658591e-01 [static]

Definition at line 73 of file e_log2.c.

double ln2 = 0.69314718055994530942 [static]

Definition at line 65 of file e_log2.c.

double two54 = 1.80143985094819840000e+16 [static]

Definition at line 66 of file e_log2.c.

double zero = 0.0 [static]

Definition at line 78 of file e_log2.c.