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Diffstat (limited to 'src/math/expm1l.c')
| -rw-r--r-- | src/math/expm1l.c | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/src/math/expm1l.c b/src/math/expm1l.c new file mode 100644 index 00000000..2f94dfa2 --- /dev/null +++ b/src/math/expm1l.c @@ -0,0 +1,123 @@ +/* origin: OpenBSD /usr/src/lib/libm/src/ld80/e_expm1l.c */ +/* + * Copyright (c) 2008 Stephen L. Moshier <steve@moshier.net> + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ +/* + * Exponential function, minus 1 + * Long double precision + * + * + * SYNOPSIS: + * + * long double x, y, expm1l(); + * + * y = expm1l( x ); + * + * + * DESCRIPTION: + * + * Returns e (2.71828...) raised to the x power, minus 1. + * + * 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 -45,+MAXLOG 200,000 1.2e-19 2.5e-20 + * + * ERROR MESSAGES: + * + * message condition value returned + * expm1l overflow x > MAXLOG MAXNUM + * + */ + +#include "libm.h" + +#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024 +long double expm1l(long double x) +{ + return expm1(x); +} +#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384 +static const long double MAXLOGL = 1.1356523406294143949492E4L; + +/* 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 = 3.4e-22 */ +static const long double +P0 = -1.586135578666346600772998894928250240826E4L, +P1 = 2.642771505685952966904660652518429479531E3L, +P2 = -3.423199068835684263987132888286791620673E2L, +P3 = 1.800826371455042224581246202420972737840E1L, +P4 = -5.238523121205561042771939008061958820811E-1L, +Q0 = -9.516813471998079611319047060563358064497E4L, +Q1 = 3.964866271411091674556850458227710004570E4L, +Q2 = -7.207678383830091850230366618190187434796E3L, +Q3 = 7.206038318724600171970199625081491823079E2L, +Q4 = -4.002027679107076077238836622982900945173E1L, +/* Q5 = 1.000000000000000000000000000000000000000E0 */ +/* C1 + C2 = ln 2 */ +C1 = 6.93145751953125E-1L, +C2 = 1.428606820309417232121458176568075500134E-6L, +/* ln 2^-65 */ +minarg = -4.5054566736396445112120088E1L, +huge = 0x1p10000L; + +long double expm1l(long double x) +{ + long double px, qx, xx; + int k; + + /* Overflow. */ + if (x > MAXLOGL) + return huge*huge; /* overflow */ + if (x == 0.0) + return x; + /* Minimum value.*/ + if (x < minarg) + return -1.0L; + + xx = C1 + C2; + /* Express x = ln 2 (k + remainder), remainder not exceeding 1/2. */ + px = floorl (0.5 + x / xx); + k = px; + /* remainder times ln 2 */ + x -= px * C1; + x -= px * C2; + + /* Approximate exp(remainder ln 2).*/ + px = (((( P4 * x + P3) * x + P2) * x + P1) * x + P0) * x; + qx = (((( 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 = ldexpl(1.0L, k); + x = px * qx + (px - 1.0); + return x; +} +#endif |