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/* origin: FreeBSD /usr/src/lib/msun/ld80/k_tanl.c */
/*
* ====================================================
* Copyright 2004 Sun Microsystems, Inc. All Rights Reserved.
* Copyright (c) 2008 Steven G. Kargl, David Schultz, Bruce D. Evans.
*
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#include "libm.h"
#if LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
/*
* ld80 version of __tan.c. See __tan.c for most comments.
*/
/*
* Domain [-0.67434, 0.67434], range ~[-2.25e-22, 1.921e-22]
* |tan(x)/x - t(x)| < 2**-71.9
*
* See __cosl.c for more details about the polynomial.
*/
static const long double
T3 = 0.333333333333333333180L, /* 0xaaaaaaaaaaaaaaa5.0p-65 */
T5 = 0.133333333333333372290L, /* 0x88888888888893c3.0p-66 */
T7 = 0.0539682539682504975744L, /* 0xdd0dd0dd0dc13ba2.0p-68 */
pio4 = 0.785398163397448309628L, /* 0xc90fdaa22168c235.0p-64 */
pio4lo = -1.25413940316708300586e-20L; /* -0xece675d1fc8f8cbb.0p-130 */
static const double
T9 = 0.021869488536312216, /* 0x1664f4882cc1c2.0p-58 */
T11 = 0.0088632355256619590, /* 0x1226e355c17612.0p-59 */
T13 = 0.0035921281113786528, /* 0x1d6d3d185d7ff8.0p-61 */
T15 = 0.0014558334756312418, /* 0x17da354aa3f96b.0p-62 */
T17 = 0.00059003538700862256, /* 0x13559358685b83.0p-63 */
T19 = 0.00023907843576635544, /* 0x1f56242026b5be.0p-65 */
T21 = 0.000097154625656538905, /* 0x1977efc26806f4.0p-66 */
T23 = 0.000038440165747303162, /* 0x14275a09b3ceac.0p-67 */
T25 = 0.000018082171885432524, /* 0x12f5e563e5487e.0p-68 */
T27 = 0.0000024196006108814377, /* 0x144c0d80cc6896.0p-71 */
T29 = 0.0000078293456938132840, /* 0x106b59141a6cb3.0p-69 */
T31 = -0.0000032609076735050182, /* -0x1b5abef3ba4b59.0p-71 */
T33 = 0.0000023261313142559411; /* 0x13835436c0c87f.0p-71 */
long double __tanl(long double x, long double y, int iy) {
long double z, r, v, w, s, a, t;
long double osign;
int i;
iy = iy == 1 ? -1 : 1; /* XXX recover original interface */
// FIXME: this is wrong, use copysign, signbit or union bithack
osign = x >= 0 ? 1.0 : -1.0; /* XXX slow, probably wrong for -0 */
if (fabsl(x) >= 0.67434) {
if (x < 0) {
x = -x;
y = -y;
}
z = pio4 - x;
w = pio4lo - y;
x = z + w;
y = 0.0;
i = 1;
} else
i = 0;
z = x * x;
w = z * z;
r = T5 + w * (T9 + w * (T13 + w * (T17 + w * (T21 +
w * (T25 + w * (T29 + w * T33))))));
v = z * (T7 + w * (T11 + w * (T15 + w * (T19 + w * (T23 +
w * (T27 + w * T31))))));
s = z * x;
r = y + z * (s * (r + v) + y);
r += T3 * s;
w = x + r;
if (i == 1) {
v = (long double)iy;
return osign * (v - 2.0 * (x - (w * w / (w + v) - r)));
}
if (iy == 1)
return w;
/*
* if allow error up to 2 ulp, simply return
* -1.0 / (x+r) here
*/
/* compute -1.0 / (x+r) accurately */
z = w;
z = z + 0x1p32 - 0x1p32;
v = r - (z - x); /* z+v = r+x */
t = a = -1.0 / w; /* a = -1.0/w */
t = t + 0x1p32 - 0x1p32;
s = 1.0 + t * z;
return t + a * (s + t * v);
}
#endif
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