text: #include <stdint.h>
  
  #define FORCE_EVAL(x) do {                        \
  	if (sizeof(x) == sizeof(float)) {         \
  		volatile float __x;               \
  		__x = (x);                        \
  	} else if (sizeof(x) == sizeof(double)) { \
  		volatile double __x;              \
  		__x = (x);                        \
  	} else {                                  \
  		volatile long double __x;         \
  		__x = (x);                        \
  	}                                         \
  } while(0)
  
  /* Get two 32 bit ints from a double.  */
  #define EXTRACT_WORDS(hi,lo,d)                    \
  do {                                              \
    union {double f; uint64_t i;} __u;              \
    __u.f = (d);                                    \
    (hi) = __u.i >> 32;                             \
    (lo) = (uint32_t)__u.i;                         \
  } while (0)
  
  /* Get the more significant 32 bit int from a double.  */
  #define GET_HIGH_WORD(hi,d)                       \
  do {                                              \
    union {double f; uint64_t i;} __u;              \
    __u.f = (d);                                    \
    (hi) = __u.i >> 32;                             \
  } while (0)
  
  /* Get the less significant 32 bit int from a double.  */
  #define GET_LOW_WORD(lo,d)                        \
  do {                                              \
    union {double f; uint64_t i;} __u;              \
    __u.f = (d);                                    \
    (lo) = (uint32_t)__u.i;                         \
  } while (0)
  
  /* Set a double from two 32 bit ints.  */
  #define INSERT_WORDS(d,hi,lo)                     \
  do {                                              \
    union {double f; uint64_t i;} __u;              \
    __u.i = ((uint64_t)(hi)<<32) | (uint32_t)(lo);  \
    (d) = __u.f;                                    \
  } while (0)
  
  /* Set the more significant 32 bits of a double from an int.  */
  #define SET_HIGH_WORD(d,hi)                       \
  do {                                              \
    union {double f; uint64_t i;} __u;              \
    __u.f = (d);                                    \
    __u.i &= 0xffffffff;                            \
    __u.i |= (uint64_t)(hi) << 32;                  \
    (d) = __u.f;                                    \
  } while (0)
  
  /* Set the less significant 32 bits of a double from an int.  */
  #define SET_LOW_WORD(d,lo)                        \
  do {                                              \
    union {double f; uint64_t i;} __u;              \
    __u.f = (d);                                    \
    __u.i &= 0xffffffff00000000ull;                 \
    __u.i |= (uint32_t)(lo);                        \
    (d) = __u.f;                                    \
  } while (0)
  
  /* Get a 32 bit int from a float.  */
  #define GET_FLOAT_WORD(w,d)                       \
  do {                                              \
    union {float f; uint32_t i;} __u;               \
    __u.f = (d);                                    \
    (w) = __u.i;                                    \
  } while (0)
  
  /* Set a float from a 32 bit int.  */
  #define SET_FLOAT_WORD(d,w)                       \
  do {                                              \
    union {float f; uint32_t i;} __u;               \
    __u.i = (w);                                    \
    (d) = __u.f;                                    \
  } while (0)
  
  double sqrt(double d);
  double fabs(double d);
  double scalbn(double x, int n);
  
  static const double
  bp[]   = {1.0, 1.5,},
  dp_h[] = { 0.0, 5.84962487220764160156e-01,}, /* 0x3FE2B803, 0x40000000 */
  dp_l[] = { 0.0, 1.35003920212974897128e-08,}, /* 0x3E4CFDEB, 0x43CFD006 */
  two53  =  9007199254740992.0, /* 0x43400000, 0x00000000 */
  huge   =  1.0e300,
  tiny   =  1.0e-300,
  /* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */
  L1 =  5.99999999999994648725e-01, /* 0x3FE33333, 0x33333303 */
  L2 =  4.28571428578550184252e-01, /* 0x3FDB6DB6, 0xDB6FABFF */
  L3 =  3.33333329818377432918e-01, /* 0x3FD55555, 0x518F264D */
  L4 =  2.72728123808534006489e-01, /* 0x3FD17460, 0xA91D4101 */
  L5 =  2.30660745775561754067e-01, /* 0x3FCD864A, 0x93C9DB65 */
  L6 =  2.06975017800338417784e-01, /* 0x3FCA7E28, 0x4A454EEF */
  P1 =  1.66666666666666019037e-01, /* 0x3FC55555, 0x5555553E */
  P2 = -2.77777777770155933842e-03, /* 0xBF66C16C, 0x16BEBD93 */
  P3 =  6.61375632143793436117e-05, /* 0x3F11566A, 0xAF25DE2C */
  P4 = -1.65339022054652515390e-06, /* 0xBEBBBD41, 0xC5D26BF1 */
  P5 =  4.13813679705723846039e-08, /* 0x3E663769, 0x72BEA4D0 */
  lg2     =  6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
  lg2_h   =  6.93147182464599609375e-01, /* 0x3FE62E43, 0x00000000 */
  lg2_l   = -1.90465429995776804525e-09, /* 0xBE205C61, 0x0CA86C39 */
  ovt     =  8.0085662595372944372e-017, /* -(1024-log2(ovfl+.5ulp)) */
  cp      =  9.61796693925975554329e-01, /* 0x3FEEC709, 0xDC3A03FD =2/(3ln2) */
  cp_h    =  9.61796700954437255859e-01, /* 0x3FEEC709, 0xE0000000 =(float)cp */
  cp_l    = -7.02846165095275826516e-09, /* 0xBE3E2FE0, 0x145B01F5 =tail of cp_h*/
  ivln2   =  1.44269504088896338700e+00, /* 0x3FF71547, 0x652B82FE =1/ln2 */
  ivln2_h =  1.44269502162933349609e+00, /* 0x3FF71547, 0x60000000 =24b 1/ln2*/
  ivln2_l =  1.92596299112661746887e-08; /* 0x3E54AE0B, 0xF85DDF44 =1/ln2 tail*/
  
  double pow(double x, double y)
  {
  	double z,ax,z_h,z_l,p_h,p_l;
  	double y1,t1,t2,r,s,t,u,v,w;
  	int32_t i,j,k,yisint,n;
  	int32_t hx,hy,ix,iy;
  	uint32_t lx,ly;
  
  	EXTRACT_WORDS(hx, lx, x);
  	EXTRACT_WORDS(hy, ly, y);
  	ix = hx & 0x7fffffff;
  	iy = hy & 0x7fffffff;
  
  	/* x**0 = 1, even if x is NaN */
  	if ((iy|ly) == 0)
  		return 1.0;
  	/* 1**y = 1, even if y is NaN */
  	if (hx == 0x3ff00000 && lx == 0)
  		return 1.0;
  	/* NaN if either arg is NaN */
  	if (ix > 0x7ff00000 || (ix == 0x7ff00000 && lx != 0) ||
  	    iy > 0x7ff00000 || (iy == 0x7ff00000 && ly != 0))
  		return x + y;
  
  	/* determine if y is an odd int when x < 0
  	 * yisint = 0       ... y is not an integer
  	 * yisint = 1       ... y is an odd int
  	 * yisint = 2       ... y is an even int
  	 */
  	yisint = 0;
  	if (hx < 0) {
  		if (iy >= 0x43400000)
  			yisint = 2; /* even integer y */
  		else if (iy >= 0x3ff00000) {
  			k = (iy>>20) - 0x3ff;  /* exponent */
  			if (k > 20) {
  				j = ly>>(52-k);
  				if ((j<<(52-k)) == ly)
  					yisint = 2 - (j&1);
  			} else if (ly == 0) {
  				j = iy>>(20-k);
  				if ((j<<(20-k)) == iy)
  					yisint = 2 - (j&1);
  			}
  		}
  	}
  
  	/* special value of y */
  	if (ly == 0) {
  		if (iy == 0x7ff00000) {  /* y is +-inf */
  			if (((ix-0x3ff00000)|lx) == 0)  /* (-1)**+-inf is 1 */
  				return 1.0;
  			else if (ix >= 0x3ff00000) /* (|x|>1)**+-inf = inf,0 */
  				return hy >= 0 ? y : 0.0;
  			else if ((ix|lx) != 0)     /* (|x|<1)**+-inf = 0,inf if x!=0 */
  				return hy >= 0 ? 0.0 : -y;
  		}
  		if (iy == 0x3ff00000) {    /* y is +-1 */
  			if (hy >= 0)
  				return x;
  			y = 1/x;
  #if FLT_EVAL_METHOD!=0
  			{
  				union {double f; uint64_t i;} u = {y};
  				uint64_t i = u.i & -1ULL/2;
  				if (i>>52 == 0 && (i&(i-1)))
  					FORCE_EVAL((float)y);
  			}
  #endif
  			return y;
  		}
  		if (hy == 0x40000000)    /* y is 2 */
  			return x*x;
  		if (hy == 0x3fe00000) {  /* y is 0.5 */
  			if (hx >= 0)     /* x >= +0 */
  				return sqrt(x);
  		}
  	}
  
  	ax = fabs(x);
  	/* special value of x */
  	if (lx == 0) {
  		if (ix == 0x7ff00000 || ix == 0 || ix == 0x3ff00000) { /* x is +-0,+-inf,+-1 */
  			z = ax;
  			if (hy < 0)   /* z = (1/|x|) */
  				z = 1.0/z;
  			if (hx < 0) {
  				if (((ix-0x3ff00000)|yisint) == 0) {
  					z = (z-z)/(z-z); /* (-1)**non-int is NaN */
  				} else if (yisint == 1)
  					z = -z;          /* (x<0)**odd = -(|x|**odd) */
  			}
  			return z;
  		}
  	}
  
  	s = 1.0; /* sign of result */
  	if (hx < 0) {
  		if (yisint == 0) /* (x<0)**(non-int) is NaN */
  			return (x-x)/(x-x);
  		if (yisint == 1) /* (x<0)**(odd int) */
  			s = -1.0;
  	}
  
  	/* |y| is huge */
  	if (iy > 0x41e00000) { /* if |y| > 2**31 */
  		if (iy > 0x43f00000) {  /* if |y| > 2**64, must o/uflow */
  			if (ix <= 0x3fefffff)
  				return hy < 0 ? huge*huge : tiny*tiny;
  			if (ix >= 0x3ff00000)
  				return hy > 0 ? huge*huge : tiny*tiny;
  		}
  		/* over/underflow if x is not close to one */
  		if (ix < 0x3fefffff)
  			return hy < 0 ? s*huge*huge : s*tiny*tiny;
  		if (ix > 0x3ff00000)
  			return hy > 0 ? s*huge*huge : s*tiny*tiny;
  		/* now |1-x| is tiny <= 2**-20, suffice to compute
  		   log(x) by x-x^2/2+x^3/3-x^4/4 */
  		t = ax - 1.0;       /* t has 20 trailing zeros */
  		w = (t*t)*(0.5 - t*(0.3333333333333333333333-t*0.25));
  		u = ivln2_h*t;      /* ivln2_h has 21 sig. bits */
  		v = t*ivln2_l - w*ivln2;
  		t1 = u + v;
  		SET_LOW_WORD(t1, 0);
  		t2 = v - (t1-u);
  	} else {
  		double ss,s2,s_h,s_l,t_h,t_l;
  		n = 0;
  		/* take care subnormal number */
  		if (ix < 0x00100000) {
  			ax *= two53;
  			n -= 53;
  			GET_HIGH_WORD(ix,ax);
  		}
  		n += ((ix)>>20) - 0x3ff;
  		j = ix & 0x000fffff;
  		/* determine interval */
  		ix = j | 0x3ff00000;   /* normalize ix */
  		if (j <= 0x3988E)      /* |x|<sqrt(3/2) */
  			k = 0;
  		else if (j < 0xBB67A)  /* |x|<sqrt(3)   */
  			k = 1;
  		else {
  			k = 0;
  			n += 1;
  			ix -= 0x00100000;
  		}
  		SET_HIGH_WORD(ax, ix);
  
  		/* compute ss = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
  		u = ax - bp[k];        /* bp[0]=1.0, bp[1]=1.5 */
  		v = 1.0/(ax+bp[k]);
  		ss = u*v;
  		s_h = ss;
  		SET_LOW_WORD(s_h, 0);
  		/* t_h=ax+bp[k] High */
  		t_h = 0.0;
  		SET_HIGH_WORD(t_h, ((ix>>1)|0x20000000) + 0x00080000 + (k<<18));
  		t_l = ax - (t_h-bp[k]);
  		s_l = v*((u-s_h*t_h)-s_h*t_l);
  		/* compute log(ax) */
  		s2 = ss*ss;
  		r = s2*s2*(L1+s2*(L2+s2*(L3+s2*(L4+s2*(L5+s2*L6)))));
  		r += s_l*(s_h+ss);
  		s2 = s_h*s_h;
  		t_h = 3.0 + s2 + r;
  		SET_LOW_WORD(t_h, 0);
  		t_l = r - ((t_h-3.0)-s2);
  		/* u+v = ss*(1+...) */
  		u = s_h*t_h;
  		v = s_l*t_h + t_l*ss;
  		/* 2/(3log2)*(ss+...) */
  		p_h = u + v;
  		SET_LOW_WORD(p_h, 0);
  		p_l = v - (p_h-u);
  		z_h = cp_h*p_h;        /* cp_h+cp_l = 2/(3*log2) */
  		z_l = cp_l*p_h+p_l*cp + dp_l[k];
  		/* log2(ax) = (ss+..)*2/(3*log2) = n + dp_h + z_h + z_l */
  		t = (double)n;
  		t1 = ((z_h + z_l) + dp_h[k]) + t;
  		SET_LOW_WORD(t1, 0);
  		t2 = z_l - (((t1 - t) - dp_h[k]) - z_h);
  	}
  
  	/* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
  	y1 = y;
  	SET_LOW_WORD(y1, 0);
  	p_l = (y-y1)*t1 + y*t2;
  	p_h = y1*t1;
  	z = p_l + p_h;
  	EXTRACT_WORDS(j, i, z);
  	if (j >= 0x40900000) {                      /* z >= 1024 */
  		if (((j-0x40900000)|i) != 0)        /* if z > 1024 */
  			return s*huge*huge;         /* overflow */
  		if (p_l + ovt > z - p_h)
  			return s*huge*huge;         /* overflow */
  	} else if ((j&0x7fffffff) >= 0x4090cc00) {  /* z <= -1075 */  // FIXME: instead of abs(j) use unsigned j
  		if (((j-0xc090cc00)|i) != 0)        /* z < -1075 */
  			return s*tiny*tiny;         /* underflow */
  		if (p_l <= z - p_h)
  			return s*tiny*tiny;         /* underflow */
  	}
  	/*
  	 * compute 2**(p_h+p_l)
  	 */
  	i = j & 0x7fffffff;
  	k = (i>>20) - 0x3ff;
  	n = 0;
  	if (i > 0x3fe00000) {  /* if |z| > 0.5, set n = [z+0.5] */
  		n = j + (0x00100000>>(k+1));
  		k = ((n&0x7fffffff)>>20) - 0x3ff;  /* new k for n */
  		t = 0.0;
  		SET_HIGH_WORD(t, n & ~(0x000fffff>>k));
  		n = ((n&0x000fffff)|0x00100000)>>(20-k);
  		if (j < 0)
  			n = -n;
  		p_h -= t;
  	}
  	t = p_l + p_h;
  	SET_LOW_WORD(t, 0);
  	u = t*lg2_h;
  	v = (p_l-(t-p_h))*lg2 + t*lg2_l;
  	z = u + v;
  	w = v - (z-u);
  	t = z*z;
  	t1 = z - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
  	r = (z*t1)/(t1-2.0) - (w + z*w);
  	z = 1.0 - (r-z);
  	GET_HIGH_WORD(j, z);
  	j += n<<20;
  	if ((j>>20) <= 0)  /* subnormal output */
  		z = scalbn(z,n);
  	else
  		SET_HIGH_WORD(z, j);
  	return s*z;
  }
  
  