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Diffstat (limited to 'libquadmath/math/expm1q.c')
| -rw-r--r-- | libquadmath/math/expm1q.c | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/libquadmath/math/expm1q.c b/libquadmath/math/expm1q.c new file mode 100644 index 00000000000..510c98fe493 --- /dev/null +++ b/libquadmath/math/expm1q.c @@ -0,0 +1,158 @@ +/* expm1l.c + * + * Exponential function, minus 1 + * 128-bit __float128 precision + * + * + * + * SYNOPSIS: + * + * __float128 x, y, expm1l(); + * + * y = expm1l( x ); + * + * + * + * DESCRIPTION: + * + * Returns e (2.71828...) raised to the x power, minus one. + * + * Range reduction is accomplished by separating the argument + * into an integer k and fraction f such that + * + * x k f + * e = 2 e. + * + * An expansion x + .5 x^2 + x^3 R(x) approximates exp(f) - 1 + * in the basic range [-0.5 ln 2, 0.5 ln 2]. + * + * + * ACCURACY: + * + * Relative error: + * arithmetic domain # trials peak rms + * IEEE -79,+MAXLOG 100,000 1.7e-34 4.5e-35 + * + */ + +/* Copyright 2001 by Stephen L. Moshier + + This library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + This library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with this library; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ + + + +#include "quadmath-imp.h" + +/* exp(x) - 1 = x + 0.5 x^2 + x^3 P(x)/Q(x) + -.5 ln 2 < x < .5 ln 2 + Theoretical peak relative error = 8.1e-36 */ + +static const __float128 + P0 = 2.943520915569954073888921213330863757240E8Q, + P1 = -5.722847283900608941516165725053359168840E7Q, + P2 = 8.944630806357575461578107295909719817253E6Q, + P3 = -7.212432713558031519943281748462837065308E5Q, + P4 = 4.578962475841642634225390068461943438441E4Q, + P5 = -1.716772506388927649032068540558788106762E3Q, + P6 = 4.401308817383362136048032038528753151144E1Q, + P7 = -4.888737542888633647784737721812546636240E-1Q, + Q0 = 1.766112549341972444333352727998584753865E9Q, + Q1 = -7.848989743695296475743081255027098295771E8Q, + Q2 = 1.615869009634292424463780387327037251069E8Q, + Q3 = -2.019684072836541751428967854947019415698E7Q, + Q4 = 1.682912729190313538934190635536631941751E6Q, + Q5 = -9.615511549171441430850103489315371768998E4Q, + Q6 = 3.697714952261803935521187272204485251835E3Q, + Q7 = -8.802340681794263968892934703309274564037E1Q, + /* Q8 = 1.000000000000000000000000000000000000000E0 */ +/* C1 + C2 = ln 2 */ + + C1 = 6.93145751953125E-1Q, + C2 = 1.428606820309417232121458176568075500134E-6Q, +/* ln (2^16384 * (1 - 2^-113)) */ + maxlog = 1.1356523406294143949491931077970764891253E4Q, +/* ln 2^-114 */ + minarg = -7.9018778583833765273564461846232128760607E1Q; + + +__float128 +expm1q (__float128 x) +{ + __float128 px, qx, xx; + int32_t ix, sign; + ieee854_float128 u; + int k; + + /* Detect infinity and NaN. */ + u.value = x; + ix = u.words32.w0; + sign = ix & 0x80000000; + ix &= 0x7fffffff; + if (ix >= 0x7fff0000) + { + /* Infinity. */ + if (((ix & 0xffff) | u.words32.w1 | u.words32.w2 | u.words32.w3) == 0) + { + if (sign) + return -1.0Q; + else + return x; + } + /* NaN. No invalid exception. */ + return x; + } + + /* expm1(+- 0) = +- 0. */ + if ((ix == 0) && (u.words32.w1 | u.words32.w2 | u.words32.w3) == 0) + return x; + + /* Overflow. */ + if (x > maxlog) + return (HUGE_VALQ * HUGE_VALQ); + + /* Minimum value. */ + if (x < minarg) + return (4.0/HUGE_VALQ - 1.0Q); + + /* Express x = ln 2 (k + remainder), remainder not exceeding 1/2. */ + xx = C1 + C2; /* ln 2. */ + px = floorq (0.5 + x / xx); + k = px; + /* remainder times ln 2 */ + x -= px * C1; + x -= px * C2; + + /* Approximate exp(remainder ln 2). */ + px = (((((((P7 * x + + P6) * x + + P5) * x + P4) * x + P3) * x + P2) * x + P1) * x + P0) * x; + + qx = (((((((x + + Q7) * x + + Q6) * x + Q5) * x + Q4) * x + Q3) * x + Q2) * x + Q1) * x + Q0; + + xx = x * x; + qx = x + (0.5 * xx + xx * px / qx); + + /* exp(x) = exp(k ln 2) exp(remainder ln 2) = 2^k exp(remainder ln 2). + + We have qx = exp(remainder ln 2) - 1, so + exp(x) - 1 = 2^k (qx + 1) - 1 + = 2^k qx + 2^k - 1. */ + + px = ldexpq (1.0Q, k); + x = px * qx + (px - 1.0); + return x; +} |