2 * Copyright (c) 2013 Bruce D. Evans
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice unmodified, this list of conditions, and the following
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 #include <sys/cdefs.h>
36 #include "math_private.h"
38 #define MANT_DIG LDBL_MANT_DIG
39 #define MAX_EXP LDBL_MAX_EXP
40 #define MIN_EXP LDBL_MIN_EXP
43 ln2_hi = 6.9314718055829871e-1; /* 0x162e42fefa0000.0p-53 */
45 #if LDBL_MANT_DIG == 64
46 #define MULT_REDUX 0x1p32 /* exponent MANT_DIG / 2 rounded up */
48 ln2l_lo = 1.6465949582897082e-12; /* 0x1cf79abc9e3b3a.0p-92 */
49 #elif LDBL_MANT_DIG == 113
50 #define MULT_REDUX 0x1p57
51 static const long double
52 ln2l_lo = 1.64659495828970812809844307550013433e-12L; /* 0x1cf79abc9e3b39803f2f6af40f343.0p-152L */
54 #error "Unsupported long double format"
58 clogl(long double complex z)
60 long double ax, ax2h, ax2l, axh, axl, ay, ay2h, ay2l, ayh, ayl;
61 long double sh, sl, t;
66 ENTERIT(long double complex);
80 GET_LDBL_EXPSIGN(hax, ax);
82 GET_LDBL_EXPSIGN(hay, ay);
85 /* Handle NaNs and Infs using the general formula. */
86 if (kx == MAX_EXP || ky == MAX_EXP)
87 RETURNI(CMPLXL(logl(hypotl(x, y)), v));
89 /* Avoid spurious underflow, and reduce inaccuracies when ax is 1. */
91 if (ky < (MIN_EXP - 1) / 2)
92 RETURNI(CMPLXL((ay / 2) * ay, v));
93 RETURNI(CMPLXL(log1pl(ay * ay) / 2, v));
96 /* Avoid underflow when ax is not small. Also handle zero args. */
97 if (kx - ky > MANT_DIG || ay == 0)
98 RETURNI(CMPLXL(logl(ax), v));
100 /* Avoid overflow. */
101 if (kx >= MAX_EXP - 1)
102 RETURNI(CMPLXL(logl(hypotl(x * 0x1p-16382L, y * 0x1p-16382L)) +
103 (MAX_EXP - 2) * ln2l_lo + (MAX_EXP - 2) * ln2_hi, v));
104 if (kx >= (MAX_EXP - 1) / 2)
105 RETURNI(CMPLXL(logl(hypotl(x, y)), v));
107 /* Reduce inaccuracies and avoid underflow when ax is denormal. */
108 if (kx <= MIN_EXP - 2)
109 RETURNI(CMPLXL(logl(hypotl(x * 0x1p16383L, y * 0x1p16383L)) +
110 (MIN_EXP - 2) * ln2l_lo + (MIN_EXP - 2) * ln2_hi, v));
112 /* Avoid remaining underflows (when ax is small but not denormal). */
113 if (ky < (MIN_EXP - 1) / 2 + MANT_DIG)
114 RETURNI(CMPLXL(logl(hypotl(x, y)), v));
116 /* Calculate ax*ax and ay*ay exactly using Dekker's algorithm. */
117 t = (long double)(ax * (MULT_REDUX + 1));
118 axh = (long double)(ax - t) + t;
121 ax2l = axh * axh - ax2h + 2 * axh * axl + axl * axl;
122 t = (long double)(ay * (MULT_REDUX + 1));
123 ayh = (long double)(ay - t) + t;
126 ay2l = ayh * ayh - ay2h + 2 * ayh * ayl + ayl * ayl;
129 * When log(|z|) is far from 1, accuracy in calculating the sum
130 * of the squares is not very important since log() reduces
131 * inaccuracies. We depended on this to use the general
132 * formula when log(|z|) is very far from 1. When log(|z|) is
133 * moderately far from 1, we go through the extra-precision
134 * calculations to reduce branches and gain a little accuracy.
136 * When |z| is near 1, we subtract 1 and use log1p() and don't
137 * leave it to log() to subtract 1, since we gain at least 1 bit
138 * of accuracy in this way.
140 * When |z| is very near 1, subtracting 1 can cancel almost
141 * 3*MANT_DIG bits. We arrange that subtracting 1 is exact in
142 * doubled precision, and then do the rest of the calculation
143 * in sloppy doubled precision. Although large cancellations
144 * often lose lots of accuracy, here the final result is exact
145 * in doubled precision if the large calculation occurs (because
146 * then it is exact in tripled precision and the cancellation
147 * removes enough bits to fit in doubled precision). Thus the
148 * result is accurate in sloppy doubled precision, and the only
149 * significant loss of accuracy is when it is summed and passed
155 if (sh < 0.5 || sh >= 3)
156 RETURNI(CMPLXL(logl(ay2l + ax2l + sl + sh) / 2, v));
160 /* Briggs-Kahan algorithm (except we discard the final low term): */
165 RETURNI(CMPLXL(log1pl(ay2l + t + sh) / 2, v));