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+/* origin: FreeBSD /usr/src/lib/msun/src/e_pow.c */
+/*
+ * ====================================================
+ * Copyright (C) 2004 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+/* pow(x,y) return x**y
+ *
+ * n
+ * Method: Let x = 2 * (1+f)
+ * 1. Compute and return log2(x) in two pieces:
+ * log2(x) = w1 + w2,
+ * where w1 has 53-24 = 29 bit trailing zeros.
+ * 2. Perform y*log2(x) = n+y' by simulating muti-precision
+ * arithmetic, where |y'|<=0.5.
+ * 3. Return x**y = 2**n*exp(y'*log2)
+ *
+ * Special cases:
+ * 1. (anything) ** 0 is 1
+ * 2. (anything) ** 1 is itself
+ * 3. (anything except 1) ** NAN is NAN, 1 ** NAN is 1
+ * 4. NAN ** (anything except 0) is NAN
+ * 5. +-(|x| > 1) ** +INF is +INF
+ * 6. +-(|x| > 1) ** -INF is +0
+ * 7. +-(|x| < 1) ** +INF is +0
+ * 8. +-(|x| < 1) ** -INF is +INF
+ * 9. +-1 ** +-INF is 1
+ * 10. +0 ** (+anything except 0, NAN) is +0
+ * 11. -0 ** (+anything except 0, NAN, odd integer) is +0
+ * 12. +0 ** (-anything except 0, NAN) is +INF
+ * 13. -0 ** (-anything except 0, NAN, odd integer) is +INF
+ * 14. -0 ** (odd integer) = -( +0 ** (odd integer) )
+ * 15. +INF ** (+anything except 0,NAN) is +INF
+ * 16. +INF ** (-anything except 0,NAN) is +0
+ * 17. -INF ** (anything) = -0 ** (-anything)
+ * 18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer)
+ * 19. (-anything except 0 and inf) ** (non-integer) is NAN
+ *
+ * Accuracy:
+ * pow(x,y) returns x**y nearly rounded. In particular
+ * pow(integer,integer)
+ * always returns the correct integer provided it is
+ * representable.
+ *
+ * Constants :
+ * The hexadecimal values are the intended ones for the following
+ * constants. The decimal values may be used, provided that the
+ * compiler will convert from decimal to binary accurately enough
+ * to produce the hexadecimal values shown.
+ */
+
+#include "libm.h"
+
+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 */
+zero = 0.0,
+one = 1.0,
+two = 2.0,
+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;
+
+ /* y == zero: x**0 = 1 */
+ if ((iy|ly) == 0)
+ return one;
+
+ /* x == 1: 1**y = 1, even if y is NaN */
+ if (hx == 0x3ff00000 && lx == 0)
+ return one;
+
+ /* y != zero: result is NaN if either arg is NaN */
+ if (ix > 0x7ff00000 || (ix == 0x7ff00000 && lx != 0) ||
+ iy > 0x7ff00000 || (iy == 0x7ff00000 && ly != 0))
+ return (x+0.0)+(y+0.0); // FIXME: 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 one;
+ else if (ix >= 0x3ff00000) /* (|x|>1)**+-inf = inf,0 */
+ return hy >= 0 ? y : zero;
+ else /* (|x|<1)**+-inf = 0,inf */
+ return hy < 0 ? -y : zero;
+ }
+ if (iy == 0x3ff00000) { /* y is +-1 */
+ if (hy < 0)
+ return one/x;
+ return x;
+ }
+ 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 = one/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;
+ }
+ }
+
+ /* CYGNUS LOCAL + fdlibm-5.3 fix: This used to be
+ n = (hx>>31)+1;
+ but ANSI C says a right shift of a signed negative quantity is
+ implementation defined. */
+ n = ((uint32_t)hx>>31) - 1;
+
+ /* (x<0)**(non-int) is NaN */
+ if ((n|yisint) == 0)
+ return (x-x)/(x-x);
+
+ s = one; /* s (sign of result -ve**odd) = -1 else = 1 */
+ if ((n|(yisint-1)) == 0)
+ s = -one;/* (-ve)**(odd int) */
+
+ /* |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 - one; /* 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 = one/(ax+bp[k]);
+ ss = u*v;
+ s_h = ss;
+ SET_LOW_WORD(s_h, 0);
+ /* t_h=ax+bp[k] High */
+ t_h = zero;
+ 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 = zero;
+ 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-two) - (w + z*w);
+ z = one - (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;
+}
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