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Diffstat (limited to 'src/math/pow.c')
| -rw-r--r-- | src/math/pow.c | 621 |
1 files changed, 318 insertions, 303 deletions
diff --git a/src/math/pow.c b/src/math/pow.c index 3ddc1b6f..694c2ef6 100644 --- a/src/math/pow.c +++ b/src/math/pow.c @@ -1,328 +1,343 @@ -/* origin: FreeBSD /usr/src/lib/msun/src/e_pow.c */ /* - * ==================================================== - * Copyright (C) 2004 by Sun Microsystems, Inc. All rights reserved. + * Double-precision x^y function. * - * 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. 1 ** (anything) is 1 - * 3. (anything except 1) ** NAN is NAN - * 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, raise divbyzero - * 13. -0 ** (-anything except 0, NAN, odd integer) is +INF, raise divbyzero - * 14. -0 ** (+odd integer) is -0 - * 15. -0 ** (-odd integer) is -INF, raise divbyzero - * 16. +INF ** (+anything except 0,NAN) is +INF - * 17. +INF ** (-anything except 0,NAN) is +0 - * 18. -INF ** (+odd integer) is -INF - * 19. -INF ** (anything) = -0 ** (-anything), (anything except odd integer) - * 20. (anything) ** 1 is (anything) - * 21. (anything) ** -1 is 1/(anything) - * 22. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer) - * 23. (-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. + * Copyright (c) 2018, Arm Limited. + * SPDX-License-Identifier: MIT */ +#include <math.h> +#include <stdint.h> #include "libm.h" +#include "exp_data.h" +#include "pow_data.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 */ -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*/ +/* +Worst-case error: 0.54 ULP (~= ulperr_exp + 1024*Ln2*relerr_log*2^53) +relerr_log: 1.3 * 2^-68 (Relative error of log, 1.5 * 2^-68 without fma) +ulperr_exp: 0.509 ULP (ULP error of exp, 0.511 ULP without fma) +*/ -double pow(double x, double y) +#define T __pow_log_data.tab +#define A __pow_log_data.poly +#define Ln2hi __pow_log_data.ln2hi +#define Ln2lo __pow_log_data.ln2lo +#define N (1 << POW_LOG_TABLE_BITS) +#define OFF 0x3fe6955500000000 + +/* Top 12 bits of a double (sign and exponent bits). */ +static inline uint32_t top12(double x) { - 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; + return asuint64(x) >> 52; +} - EXTRACT_WORDS(hx, lx, x); - EXTRACT_WORDS(hy, ly, y); - ix = hx & 0x7fffffff; - iy = hy & 0x7fffffff; +/* Compute y+TAIL = log(x) where the rounded result is y and TAIL has about + additional 15 bits precision. IX is the bit representation of x, but + normalized in the subnormal range using the sign bit for the exponent. */ +static inline double_t log_inline(uint64_t ix, double_t *tail) +{ + /* double_t for better performance on targets with FLT_EVAL_METHOD==2. */ + double_t z, r, y, invc, logc, logctail, kd, hi, t1, t2, lo, lo1, lo2, p; + uint64_t iz, tmp; + int k, i; - /* 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; + /* x = 2^k z; where z is in range [OFF,2*OFF) and exact. + The range is split into N subintervals. + The ith subinterval contains z and c is near its center. */ + tmp = ix - OFF; + i = (tmp >> (52 - POW_LOG_TABLE_BITS)) % N; + k = (int64_t)tmp >> 52; /* arithmetic shift */ + iz = ix - (tmp & 0xfffULL << 52); + z = asdouble(iz); + kd = (double_t)k; - /* 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) { - uint32_t j = ly>>(52-k); - if ((j<<(52-k)) == ly) - yisint = 2 - (j&1); - } else if (ly == 0) { - uint32_t j = iy>>(20-k); - if ((j<<(20-k)) == iy) - yisint = 2 - (j&1); - } - } - } + /* log(x) = k*Ln2 + log(c) + log1p(z/c-1). */ + invc = T[i].invc; + logc = T[i].logc; + logctail = T[i].logctail; - /* 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 /* (|x|<1)**+-inf = 0,inf */ - 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); - } + /* Note: 1/c is j/N or j/N/2 where j is an integer in [N,2N) and + |z/c - 1| < 1/N, so r = z/c - 1 is exactly representible. */ +#if __FP_FAST_FMA + r = __builtin_fma(z, invc, -1.0); +#else + /* Split z such that rhi, rlo and rhi*rhi are exact and |rlo| <= |r|. */ + double_t zhi = asdouble((iz + (1ULL << 31)) & (-1ULL << 32)); + double_t zlo = z - zhi; + double_t rhi = zhi * invc - 1.0; + double_t rlo = zlo * invc; + r = rhi + rlo; #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); - } + + /* k*Ln2 + log(c) + r. */ + t1 = kd * Ln2hi + logc; + t2 = t1 + r; + lo1 = kd * Ln2lo + logctail; + lo2 = t1 - t2 + r; + + /* Evaluation is optimized assuming superscalar pipelined execution. */ + double_t ar, ar2, ar3, lo3, lo4; + ar = A[0] * r; /* A[0] = -0.5. */ + ar2 = r * ar; + ar3 = r * ar2; + /* k*Ln2 + log(c) + r + A[0]*r*r. */ +#if __FP_FAST_FMA + hi = t2 + ar2; + lo3 = __builtin_fma(ar, r, -ar2); + lo4 = t2 - hi + ar2; +#else + double_t arhi = A[0] * rhi; + double_t arhi2 = rhi * arhi; + hi = t2 + arhi2; + lo3 = rlo * (ar + arhi); + lo4 = t2 - hi + arhi2; +#endif + /* p = log1p(r) - r - A[0]*r*r. */ + p = (ar3 * (A[1] + r * A[2] + + ar2 * (A[3] + r * A[4] + ar2 * (A[5] + r * A[6])))); + lo = lo1 + lo2 + lo3 + lo4 + p; + y = hi + lo; + *tail = hi - y + lo; + return y; +} + +#undef N +#undef T +#define N (1 << EXP_TABLE_BITS) +#define InvLn2N __exp_data.invln2N +#define NegLn2hiN __exp_data.negln2hiN +#define NegLn2loN __exp_data.negln2loN +#define Shift __exp_data.shift +#define T __exp_data.tab +#define C2 __exp_data.poly[5 - EXP_POLY_ORDER] +#define C3 __exp_data.poly[6 - EXP_POLY_ORDER] +#define C4 __exp_data.poly[7 - EXP_POLY_ORDER] +#define C5 __exp_data.poly[8 - EXP_POLY_ORDER] +#define C6 __exp_data.poly[9 - EXP_POLY_ORDER] + +/* Handle cases that may overflow or underflow when computing the result that + is scale*(1+TMP) without intermediate rounding. The bit representation of + scale is in SBITS, however it has a computed exponent that may have + overflown into the sign bit so that needs to be adjusted before using it as + a double. (int32_t)KI is the k used in the argument reduction and exponent + adjustment of scale, positive k here means the result may overflow and + negative k means the result may underflow. */ +static inline double specialcase(double_t tmp, uint64_t sbits, uint64_t ki) +{ + double_t scale, y; + + if ((ki & 0x80000000) == 0) { + /* k > 0, the exponent of scale might have overflowed by <= 460. */ + sbits -= 1009ull << 52; + scale = asdouble(sbits); + y = 0x1p1009 * (scale + scale * tmp); + return eval_as_double(y); + } + /* k < 0, need special care in the subnormal range. */ + sbits += 1022ull << 52; + /* Note: sbits is signed scale. */ + scale = asdouble(sbits); + y = scale + scale * tmp; + if (fabs(y) < 1.0) { + /* Round y to the right precision before scaling it into the subnormal + range to avoid double rounding that can cause 0.5+E/2 ulp error where + E is the worst-case ulp error outside the subnormal range. So this + is only useful if the goal is better than 1 ulp worst-case error. */ + double_t hi, lo, one = 1.0; + if (y < 0.0) + one = -1.0; + lo = scale - y + scale * tmp; + hi = one + y; + lo = one - hi + y + lo; + y = eval_as_double(hi + lo) - one; + /* Fix the sign of 0. */ + if (y == 0.0) + y = asdouble(sbits & 0x8000000000000000); + /* The underflow exception needs to be signaled explicitly. */ + fp_force_eval(fp_barrier(0x1p-1022) * 0x1p-1022); } + y = 0x1p-1022 * y; + return eval_as_double(y); +} - 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; +#define SIGN_BIAS (0x800 << EXP_TABLE_BITS) + +/* Computes sign*exp(x+xtail) where |xtail| < 2^-8/N and |xtail| <= |x|. + The sign_bias argument is SIGN_BIAS or 0 and sets the sign to -1 or 1. */ +static inline double exp_inline(double_t x, double_t xtail, uint32_t sign_bias) +{ + uint32_t abstop; + uint64_t ki, idx, top, sbits; + /* double_t for better performance on targets with FLT_EVAL_METHOD==2. */ + double_t kd, z, r, r2, scale, tail, tmp; + + abstop = top12(x) & 0x7ff; + if (predict_false(abstop - top12(0x1p-54) >= + top12(512.0) - top12(0x1p-54))) { + if (abstop - top12(0x1p-54) >= 0x80000000) { + /* Avoid spurious underflow for tiny x. */ + /* Note: 0 is common input. */ + double_t one = WANT_ROUNDING ? 1.0 + x : 1.0; + return sign_bias ? -one : one; + } + if (abstop >= top12(1024.0)) { + /* Note: inf and nan are already handled. */ + if (asuint64(x) >> 63) + return __math_uflow(sign_bias); + else + return __math_oflow(sign_bias); } + /* Large x is special cased below. */ + abstop = 0; } - 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; - } + /* exp(x) = 2^(k/N) * exp(r), with exp(r) in [2^(-1/2N),2^(1/2N)]. */ + /* x = ln2/N*k + r, with int k and r in [-ln2/2N, ln2/2N]. */ + z = InvLn2N * x; +#if TOINT_INTRINSICS + kd = roundtoint(z); + ki = converttoint(z); +#elif EXP_USE_TOINT_NARROW + /* z - kd is in [-0.5-2^-16, 0.5] in all rounding modes. */ + kd = eval_as_double(z + Shift); + ki = asuint64(kd) >> 16; + kd = (double_t)(int32_t)ki; +#else + /* z - kd is in [-1, 1] in non-nearest rounding modes. */ + kd = eval_as_double(z + Shift); + ki = asuint64(kd); + kd -= Shift; +#endif + r = x + kd * NegLn2hiN + kd * NegLn2loN; + /* The code assumes 2^-200 < |xtail| < 2^-8/N. */ + r += xtail; + /* 2^(k/N) ~= scale * (1 + tail). */ + idx = 2 * (ki % N); + top = (ki + sign_bias) << (52 - EXP_TABLE_BITS); + tail = asdouble(T[idx]); + /* This is only a valid scale when -1023*N < k < 1024*N. */ + sbits = T[idx + 1] + top; + /* exp(x) = 2^(k/N) * exp(r) ~= scale + scale * (tail + exp(r) - 1). */ + /* Evaluation is optimized assuming superscalar pipelined execution. */ + r2 = r * r; + /* Without fma the worst case error is 0.25/N ulp larger. */ + /* Worst case error is less than 0.5+1.11/N+(abs poly error * 2^53) ulp. */ + tmp = tail + r + r2 * (C2 + r * C3) + r2 * r2 * (C4 + r * C5); + if (predict_false(abstop == 0)) + return specialcase(tmp, sbits, ki); + scale = asdouble(sbits); + /* Note: tmp == 0 or |tmp| > 2^-200 and scale > 2^-739, so there + is no spurious underflow here even without fma. */ + return eval_as_double(scale + scale * tmp); +} - /* |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; +/* Returns 0 if not int, 1 if odd int, 2 if even int. The argument is + the bit representation of a non-zero finite floating-point value. */ +static inline int checkint(uint64_t iy) +{ + int e = iy >> 52 & 0x7ff; + if (e < 0x3ff) + return 0; + if (e > 0x3ff + 52) + return 2; + if (iy & ((1ULL << (0x3ff + 52 - e)) - 1)) + return 0; + if (iy & (1ULL << (0x3ff + 52 - e))) + return 1; + return 2; +} + +/* Returns 1 if input is the bit representation of 0, infinity or nan. */ +static inline int zeroinfnan(uint64_t i) +{ + return 2 * i - 1 >= 2 * asuint64(INFINITY) - 1; +} + +double pow(double x, double y) +{ + uint32_t sign_bias = 0; + uint64_t ix, iy; + uint32_t topx, topy; + + ix = asuint64(x); + iy = asuint64(y); + topx = top12(x); + topy = top12(y); + if (predict_false(topx - 0x001 >= 0x7ff - 0x001 || + (topy & 0x7ff) - 0x3be >= 0x43e - 0x3be)) { + /* Note: if |y| > 1075 * ln2 * 2^53 ~= 0x1.749p62 then pow(x,y) = inf/0 + and if |y| < 2^-54 / 1075 ~= 0x1.e7b6p-65 then pow(x,y) = +-1. */ + /* Special cases: (x < 0x1p-126 or inf or nan) or + (|y| < 0x1p-65 or |y| >= 0x1p63 or nan). */ + if (predict_false(zeroinfnan(iy))) { + if (2 * iy == 0) + return issignaling_inline(x) ? x + y : 1.0; + if (ix == asuint64(1.0)) + return issignaling_inline(y) ? x + y : 1.0; + if (2 * ix > 2 * asuint64(INFINITY) || + 2 * iy > 2 * asuint64(INFINITY)) + return x + y; + if (2 * ix == 2 * asuint64(1.0)) + return 1.0; + if ((2 * ix < 2 * asuint64(1.0)) == !(iy >> 63)) + return 0.0; /* |x|<1 && y==inf or |x|>1 && y==-inf. */ + return y * y; } - /* 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); + if (predict_false(zeroinfnan(ix))) { + double_t x2 = x * x; + if (ix >> 63 && checkint(iy) == 1) + x2 = -x2; + /* Without the barrier some versions of clang hoist the 1/x2 and + thus division by zero exception can be signaled spuriously. */ + return iy >> 63 ? fp_barrier(1 / x2) : x2; } - 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; + /* Here x and y are non-zero finite. */ + if (ix >> 63) { + /* Finite x < 0. */ + int yint = checkint(iy); + if (yint == 0) + return __math_invalid(x); + if (yint == 1) + sign_bias = SIGN_BIAS; + ix &= 0x7fffffffffffffff; + topx &= 0x7ff; + } + if ((topy & 0x7ff) - 0x3be >= 0x43e - 0x3be) { + /* Note: sign_bias == 0 here because y is not odd. */ + if (ix == asuint64(1.0)) + return 1.0; + if ((topy & 0x7ff) < 0x3be) { + /* |y| < 2^-65, x^y ~= 1 + y*log(x). */ + if (WANT_ROUNDING) + return ix > asuint64(1.0) ? 1.0 + y : + 1.0 - y; + else + return 1.0; + } + return (ix > asuint64(1.0)) == (topy < 0x800) ? + __math_oflow(0) : + __math_uflow(0); + } + if (topx == 0) { + /* Normalize subnormal x so exponent becomes negative. */ + ix = asuint64(x * 0x1p52); + ix &= 0x7fffffffffffffff; + ix -= 52ULL << 52; } - 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; + double_t lo; + double_t hi = log_inline(ix, &lo); + double_t ehi, elo; +#if __FP_FAST_FMA + ehi = y * hi; + elo = y * lo + __builtin_fma(y, hi, -ehi); +#else + double_t yhi = asdouble(iy & -1ULL << 27); + double_t ylo = y - yhi; + double_t lhi = asdouble(asuint64(hi) & -1ULL << 27); + double_t llo = hi - lhi + lo; + ehi = yhi * lhi; + elo = ylo * lhi + y * llo; /* |elo| < |ehi| * 2^-25. */ +#endif + return exp_inline(ehi, elo, sign_bias); } |