2 * SPDX-License-Identifier: BSD-2-Clause
4 * Copyright (c) 2009-2013 Steven G. Kargl
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice unmodified, this list of conditions, and the following
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 * Optimized by Bruce D. Evans.
31 #include <sys/cdefs.h>
33 * Compute the exponential of x for Intel 80-bit format. This is based on:
35 * PTP Tang, "Table-driven implementation of the exponential function
36 * in IEEE floating-point arithmetic," ACM Trans. Math. Soft., 15,
39 * where the 32 table entries have been expanded to INTERVALS (see below).
50 #include "math_private.h"
53 /* XXX Prevent compilers from erroneously constant folding these: */
54 static const volatile long double
58 static const long double
59 twom10000 = 0x1p-10000L;
61 static const union IEEEl2bits
62 /* log(2**16384 - 0.5) rounded towards zero: */
63 /* log(2**16384 - 0.5 + 1) rounded towards zero for expm1l() is the same: */
64 o_thresholdu = LD80C(0xb17217f7d1cf79ab, 13, 11356.5234062941439488L),
65 #define o_threshold (o_thresholdu.e)
66 /* log(2**(-16381-64-1)) rounded towards zero: */
67 u_thresholdu = LD80C(0xb21dfe7f09e2baa9, 13, -11399.4985314888605581L);
68 #define u_threshold (u_thresholdu.e)
74 long double hi, lo, t, twopk;
78 /* Filter out exceptional cases. */
82 if (ix >= BIAS + 13) { /* |x| >= 8192 or x is NaN */
83 if (ix == BIAS + LDBL_MAX_EXP) {
84 if (hx & 0x8000) /* x is -Inf, -NaN or unsupported */
86 RETURNF(x + x); /* x is +Inf, +NaN or unsupported */
92 } else if (ix < BIAS - 75) { /* |x| < 0x1p-75 (includes pseudos) */
93 RETURNF(1 + x); /* 1 with inexact iff x != 0 */
99 __k_expl(x, &hi, &lo, &k);
103 if (k >= LDBL_MIN_EXP) {
104 if (k == LDBL_MAX_EXP)
105 RETURNI(t * 2 * 0x1p16383L);
106 SET_LDBL_EXPSIGN(twopk, BIAS + k);
109 SET_LDBL_EXPSIGN(twopk, BIAS + k + 10000);
110 RETURNI(t * twopk * twom10000);
115 * Compute expm1l(x) for Intel 80-bit format. This is based on:
117 * PTP Tang, "Table-driven implementation of the Expm1 function
118 * in IEEE floating-point arithmetic," ACM Trans. Math. Soft., 18,
123 * Our T1 and T2 are chosen to be approximately the points where method
124 * A and method B have the same accuracy. Tang's T1 and T2 are the
125 * points where method A's accuracy changes by a full bit. For Tang,
126 * this drop in accuracy makes method A immediately less accurate than
127 * method B, but our larger INTERVALS makes method A 2 bits more
128 * accurate so it remains the most accurate method significantly
129 * closer to the origin despite losing the full bit in our extended
133 T1 = -0.1659, /* ~-30.625/128 * log(2) */
134 T2 = 0.1659; /* ~30.625/128 * log(2) */
137 * Domain [-0.1659, 0.1659], range ~[-2.6155e-22, 2.5507e-23]:
138 * |(exp(x)-1-x-x**2/2)/x - p(x)| < 2**-71.6
140 * XXX the coeffs aren't very carefully rounded, and I get 2.8 more bits,
141 * but unlike for ld128 we can't drop any terms.
143 static const union IEEEl2bits
144 B3 = LD80C(0xaaaaaaaaaaaaaaab, -3, 1.66666666666666666671e-1L),
145 B4 = LD80C(0xaaaaaaaaaaaaaaac, -5, 4.16666666666666666712e-2L);
148 B5 = 8.3333333333333245e-3, /* 0x1.111111111110cp-7 */
149 B6 = 1.3888888888888861e-3, /* 0x1.6c16c16c16c0ap-10 */
150 B7 = 1.9841269841532042e-4, /* 0x1.a01a01a0319f9p-13 */
151 B8 = 2.4801587302069236e-5, /* 0x1.a01a01a03cbbcp-16 */
152 B9 = 2.7557316558468562e-6, /* 0x1.71de37fd33d67p-19 */
153 B10 = 2.7557315829785151e-7, /* 0x1.27e4f91418144p-22 */
154 B11 = 2.5063168199779829e-8, /* 0x1.ae94fabdc6b27p-26 */
155 B12 = 2.0887164654459567e-9; /* 0x1.1f122d6413fe1p-29 */
158 expm1l(long double x)
160 union IEEEl2bits u, v;
161 long double fn, hx2_hi, hx2_lo, q, r, r1, r2, t, twomk, twopk, x_hi;
162 long double x_lo, x2, z;
167 /* Filter out exceptional cases. */
169 hx = u.xbits.expsign;
171 if (ix >= BIAS + 6) { /* |x| >= 64 or x is NaN */
172 if (ix == BIAS + LDBL_MAX_EXP) {
173 if (hx & 0x8000) /* x is -Inf, -NaN or unsupported */
175 RETURNF(x + x); /* x is +Inf, +NaN or unsupported */
178 RETURNF(huge * huge);
180 * expm1l() never underflows, but it must avoid
181 * unrepresentable large negative exponents. We used a
182 * much smaller threshold for large |x| above than in
183 * expl() so as to handle not so large negative exponents
184 * in the same way as large ones here.
186 if (hx & 0x8000) /* x <= -64 */
187 RETURNF(tiny - 1); /* good for x < -65ln2 - eps */
192 if (T1 < x && x < T2) {
193 if (ix < BIAS - 74) { /* |x| < 0x1p-74 (includes pseudos) */
194 /* x (rounded) with inexact if x != 0: */
196 (0x1p100 * x + fabsl(x)) * 0x1p-100);
203 * XXX the number of terms is no longer good for
204 * pairwise grouping of all except B3, and the
205 * grouping is no longer from highest down.
207 (x2 * B12 + (x * B11 + B10)) +
208 (x2 * (x * B9 + B8) + (x * B7 + B6))) +
209 (x * B5 + B4.e)) + x2 * x * B3.e;
213 hx2_hi = x_hi * x_hi / 2;
214 hx2_lo = x_lo * (x + x_hi) / 2;
216 RETURNI((hx2_hi + x_hi) + (hx2_lo + x_lo + q));
218 RETURNI(x + (hx2_lo + q + hx2_hi));
221 /* Reduce x to (k*ln2 + endpoint[n2] + r1 + r2). */
222 fn = rnintl(x * INV_L);
224 n2 = (unsigned)n % INTERVALS;
225 k = n >> LOG2_INTERVALS;
230 /* Prepare scale factor. */
232 v.xbits.expsign = BIAS + k;
236 * Evaluate lower terms of
237 * expl(endpoint[n2] + r1 + r2) = tbl[n2] * expl(r1 + r2).
240 q = r2 + z * (A2 + r * A3) + z * z * (A4 + r * A5) + z * z * z * A6;
242 t = (long double)tbl[n2].lo + tbl[n2].hi;
245 t = SUM2P(tbl[n2].hi - 1, tbl[n2].lo * (r1 + 1) + t * q +
250 t = SUM2P(tbl[n2].hi - 2, tbl[n2].lo * (r1 + 1) + t * q +
255 t = SUM2P(tbl[n2].hi, tbl[n2].lo + t * (q + r1));
256 RETURNI(t * twopk - 1);
258 if (k > 2 * LDBL_MANT_DIG - 1) {
259 t = SUM2P(tbl[n2].hi, tbl[n2].lo + t * (q + r1));
260 if (k == LDBL_MAX_EXP)
261 RETURNI(t * 2 * 0x1p16383L - 1);
262 RETURNI(t * twopk - 1);
265 v.xbits.expsign = BIAS - k;
268 if (k > LDBL_MANT_DIG - 1)
269 t = SUM2P(tbl[n2].hi, tbl[n2].lo - twomk + t * (q + r1));
271 t = SUM2P(tbl[n2].hi - twomk, tbl[n2].lo + t * (q + r1));