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- #include "math.h"
- #include "math_private.h"
- static const double
- ln2 = 0.69314718055994530942,
- two54 = 1.80143985094819840000e+16,
- Lg1 = 6.666666666666735130e-01,
- Lg2 = 3.999999999940941908e-01,
- Lg3 = 2.857142874366239149e-01,
- Lg4 = 2.222219843214978396e-01,
- Lg5 = 1.818357216161805012e-01,
- Lg6 = 1.531383769920937332e-01,
- Lg7 = 1.479819860511658591e-01;
- static const double zero = 0.0;
- double __ieee754_log2(double x)
- {
- 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) {
- if (((hx&0x7fffffff)|lx)==0)
- return -two54/(x-x);
- if (hx<0) return (x-x)/(x-x);
- k -= 54; x *= two54;
- 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));
- k += (i>>20);
- dk = (double) k;
- f = x-1.0;
- if((0x000fffff&(2+hx))<3) {
- 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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