s_exp2.cpp (14288B)
1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2005 David Schultz <das@FreeBSD.ORG> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 //#include <sys/cdefs.h> 30 //__FBSDID("$FreeBSD$"); 31 32 #include <float.h> 33 34 #include "math_private.h" 35 36 #define TBLBITS 8 37 #define TBLSIZE (1 << TBLBITS) 38 39 static const double 40 redux = 0x1.8p52 / TBLSIZE, 41 P1 = 0x1.62e42fefa39efp-1, 42 P2 = 0x1.ebfbdff82c575p-3, 43 P3 = 0x1.c6b08d704a0a6p-5, 44 P4 = 0x1.3b2ab88f70400p-7, 45 P5 = 0x1.5d88003875c74p-10; 46 47 static volatile double 48 huge = 0x1p1000, 49 twom1000 = 0x1p-1000; 50 51 static const double tbl[TBLSIZE * 2] = { 52 /* exp2(z + eps) eps */ 53 0x1.6a09e667f3d5dp-1, 0x1.9880p-44, 54 0x1.6b052fa751744p-1, 0x1.8000p-50, 55 0x1.6c012750bd9fep-1, -0x1.8780p-45, 56 0x1.6cfdcddd476bfp-1, 0x1.ec00p-46, 57 0x1.6dfb23c651a29p-1, -0x1.8000p-50, 58 0x1.6ef9298593ae3p-1, -0x1.c000p-52, 59 0x1.6ff7df9519386p-1, -0x1.fd80p-45, 60 0x1.70f7466f42da3p-1, -0x1.c880p-45, 61 0x1.71f75e8ec5fc3p-1, 0x1.3c00p-46, 62 0x1.72f8286eacf05p-1, -0x1.8300p-44, 63 0x1.73f9a48a58152p-1, -0x1.0c00p-47, 64 0x1.74fbd35d7ccfcp-1, 0x1.f880p-45, 65 0x1.75feb564267f1p-1, 0x1.3e00p-47, 66 0x1.77024b1ab6d48p-1, -0x1.7d00p-45, 67 0x1.780694fde5d38p-1, -0x1.d000p-50, 68 0x1.790b938ac1d00p-1, 0x1.3000p-49, 69 0x1.7a11473eb0178p-1, -0x1.d000p-49, 70 0x1.7b17b0976d060p-1, 0x1.0400p-45, 71 0x1.7c1ed0130c133p-1, 0x1.0000p-53, 72 0x1.7d26a62ff8636p-1, -0x1.6900p-45, 73 0x1.7e2f336cf4e3bp-1, -0x1.2e00p-47, 74 0x1.7f3878491c3e8p-1, -0x1.4580p-45, 75 0x1.80427543e1b4ep-1, 0x1.3000p-44, 76 0x1.814d2add1071ap-1, 0x1.f000p-47, 77 0x1.82589994ccd7ep-1, -0x1.1c00p-45, 78 0x1.8364c1eb942d0p-1, 0x1.9d00p-45, 79 0x1.8471a4623cab5p-1, 0x1.7100p-43, 80 0x1.857f4179f5bbcp-1, 0x1.2600p-45, 81 0x1.868d99b4491afp-1, -0x1.2c40p-44, 82 0x1.879cad931a395p-1, -0x1.3000p-45, 83 0x1.88ac7d98a65b8p-1, -0x1.a800p-45, 84 0x1.89bd0a4785800p-1, -0x1.d000p-49, 85 0x1.8ace5422aa223p-1, 0x1.3280p-44, 86 0x1.8be05bad619fap-1, 0x1.2b40p-43, 87 0x1.8cf3216b54383p-1, -0x1.ed00p-45, 88 0x1.8e06a5e08664cp-1, -0x1.0500p-45, 89 0x1.8f1ae99157807p-1, 0x1.8280p-45, 90 0x1.902fed0282c0ep-1, -0x1.cb00p-46, 91 0x1.9145b0b91ff96p-1, -0x1.5e00p-47, 92 0x1.925c353aa2ff9p-1, 0x1.5400p-48, 93 0x1.93737b0cdc64ap-1, 0x1.7200p-46, 94 0x1.948b82b5f98aep-1, -0x1.9000p-47, 95 0x1.95a44cbc852cbp-1, 0x1.5680p-45, 96 0x1.96bdd9a766f21p-1, -0x1.6d00p-44, 97 0x1.97d829fde4e2ap-1, -0x1.1000p-47, 98 0x1.98f33e47a23a3p-1, 0x1.d000p-45, 99 0x1.9a0f170ca0604p-1, -0x1.8a40p-44, 100 0x1.9b2bb4d53ff89p-1, 0x1.55c0p-44, 101 0x1.9c49182a3f15bp-1, 0x1.6b80p-45, 102 0x1.9d674194bb8c5p-1, -0x1.c000p-49, 103 0x1.9e86319e3238ep-1, 0x1.7d00p-46, 104 0x1.9fa5e8d07f302p-1, 0x1.6400p-46, 105 0x1.a0c667b5de54dp-1, -0x1.5000p-48, 106 0x1.a1e7aed8eb8f6p-1, 0x1.9e00p-47, 107 0x1.a309bec4a2e27p-1, 0x1.ad80p-45, 108 0x1.a42c980460a5dp-1, -0x1.af00p-46, 109 0x1.a5503b23e259bp-1, 0x1.b600p-47, 110 0x1.a674a8af46213p-1, 0x1.8880p-44, 111 0x1.a799e1330b3a7p-1, 0x1.1200p-46, 112 0x1.a8bfe53c12e8dp-1, 0x1.6c00p-47, 113 0x1.a9e6b5579fcd2p-1, -0x1.9b80p-45, 114 0x1.ab0e521356fb8p-1, 0x1.b700p-45, 115 0x1.ac36bbfd3f381p-1, 0x1.9000p-50, 116 0x1.ad5ff3a3c2780p-1, 0x1.4000p-49, 117 0x1.ae89f995ad2a3p-1, -0x1.c900p-45, 118 0x1.afb4ce622f367p-1, 0x1.6500p-46, 119 0x1.b0e07298db790p-1, 0x1.fd40p-45, 120 0x1.b20ce6c9a89a9p-1, 0x1.2700p-46, 121 0x1.b33a2b84f1a4bp-1, 0x1.d470p-43, 122 0x1.b468415b747e7p-1, -0x1.8380p-44, 123 0x1.b59728de5593ap-1, 0x1.8000p-54, 124 0x1.b6c6e29f1c56ap-1, 0x1.ad00p-47, 125 0x1.b7f76f2fb5e50p-1, 0x1.e800p-50, 126 0x1.b928cf22749b2p-1, -0x1.4c00p-47, 127 0x1.ba5b030a10603p-1, -0x1.d700p-47, 128 0x1.bb8e0b79a6f66p-1, 0x1.d900p-47, 129 0x1.bcc1e904bc1ffp-1, 0x1.2a00p-47, 130 0x1.bdf69c3f3a16fp-1, -0x1.f780p-46, 131 0x1.bf2c25bd71db8p-1, -0x1.0a00p-46, 132 0x1.c06286141b2e9p-1, -0x1.1400p-46, 133 0x1.c199bdd8552e0p-1, 0x1.be00p-47, 134 0x1.c2d1cd9fa64eep-1, -0x1.9400p-47, 135 0x1.c40ab5fffd02fp-1, -0x1.ed00p-47, 136 0x1.c544778fafd15p-1, 0x1.9660p-44, 137 0x1.c67f12e57d0cbp-1, -0x1.a100p-46, 138 0x1.c7ba88988c1b6p-1, -0x1.8458p-42, 139 0x1.c8f6d9406e733p-1, -0x1.a480p-46, 140 0x1.ca3405751c4dfp-1, 0x1.b000p-51, 141 0x1.cb720dcef9094p-1, 0x1.1400p-47, 142 0x1.ccb0f2e6d1689p-1, 0x1.0200p-48, 143 0x1.cdf0b555dc412p-1, 0x1.3600p-48, 144 0x1.cf3155b5bab3bp-1, -0x1.6900p-47, 145 0x1.d072d4a0789bcp-1, 0x1.9a00p-47, 146 0x1.d1b532b08c8fap-1, -0x1.5e00p-46, 147 0x1.d2f87080d8a85p-1, 0x1.d280p-46, 148 0x1.d43c8eacaa203p-1, 0x1.1a00p-47, 149 0x1.d5818dcfba491p-1, 0x1.f000p-50, 150 0x1.d6c76e862e6a1p-1, -0x1.3a00p-47, 151 0x1.d80e316c9834ep-1, -0x1.cd80p-47, 152 0x1.d955d71ff6090p-1, 0x1.4c00p-48, 153 0x1.da9e603db32aep-1, 0x1.f900p-48, 154 0x1.dbe7cd63a8325p-1, 0x1.9800p-49, 155 0x1.dd321f301b445p-1, -0x1.5200p-48, 156 0x1.de7d5641c05bfp-1, -0x1.d700p-46, 157 0x1.dfc97337b9aecp-1, -0x1.6140p-46, 158 0x1.e11676b197d5ep-1, 0x1.b480p-47, 159 0x1.e264614f5a3e7p-1, 0x1.0ce0p-43, 160 0x1.e3b333b16ee5cp-1, 0x1.c680p-47, 161 0x1.e502ee78b3fb4p-1, -0x1.9300p-47, 162 0x1.e653924676d68p-1, -0x1.5000p-49, 163 0x1.e7a51fbc74c44p-1, -0x1.7f80p-47, 164 0x1.e8f7977cdb726p-1, -0x1.3700p-48, 165 0x1.ea4afa2a490e8p-1, 0x1.5d00p-49, 166 0x1.eb9f4867ccae4p-1, 0x1.61a0p-46, 167 0x1.ecf482d8e680dp-1, 0x1.5500p-48, 168 0x1.ee4aaa2188514p-1, 0x1.6400p-51, 169 0x1.efa1bee615a13p-1, -0x1.e800p-49, 170 0x1.f0f9c1cb64106p-1, -0x1.a880p-48, 171 0x1.f252b376bb963p-1, -0x1.c900p-45, 172 0x1.f3ac948dd7275p-1, 0x1.a000p-53, 173 0x1.f50765b6e4524p-1, -0x1.4f00p-48, 174 0x1.f6632798844fdp-1, 0x1.a800p-51, 175 0x1.f7bfdad9cbe38p-1, 0x1.abc0p-48, 176 0x1.f91d802243c82p-1, -0x1.4600p-50, 177 0x1.fa7c1819e908ep-1, -0x1.b0c0p-47, 178 0x1.fbdba3692d511p-1, -0x1.0e00p-51, 179 0x1.fd3c22b8f7194p-1, -0x1.0de8p-46, 180 0x1.fe9d96b2a23eep-1, 0x1.e430p-49, 181 0x1.0000000000000p+0, 0x0.0000p+0, 182 0x1.00b1afa5abcbep+0, -0x1.3400p-52, 183 0x1.0163da9fb3303p+0, -0x1.2170p-46, 184 0x1.02168143b0282p+0, 0x1.a400p-52, 185 0x1.02c9a3e77806cp+0, 0x1.f980p-49, 186 0x1.037d42e11bbcap+0, -0x1.7400p-51, 187 0x1.04315e86e7f89p+0, 0x1.8300p-50, 188 0x1.04e5f72f65467p+0, -0x1.a3f0p-46, 189 0x1.059b0d315855ap+0, -0x1.2840p-47, 190 0x1.0650a0e3c1f95p+0, 0x1.1600p-48, 191 0x1.0706b29ddf71ap+0, 0x1.5240p-46, 192 0x1.07bd42b72a82dp+0, -0x1.9a00p-49, 193 0x1.0874518759bd0p+0, 0x1.6400p-49, 194 0x1.092bdf66607c8p+0, -0x1.0780p-47, 195 0x1.09e3ecac6f383p+0, -0x1.8000p-54, 196 0x1.0a9c79b1f3930p+0, 0x1.fa00p-48, 197 0x1.0b5586cf988fcp+0, -0x1.ac80p-48, 198 0x1.0c0f145e46c8ap+0, 0x1.9c00p-50, 199 0x1.0cc922b724816p+0, 0x1.5200p-47, 200 0x1.0d83b23395dd8p+0, -0x1.ad00p-48, 201 0x1.0e3ec32d3d1f3p+0, 0x1.bac0p-46, 202 0x1.0efa55fdfa9a6p+0, -0x1.4e80p-47, 203 0x1.0fb66affed2f0p+0, -0x1.d300p-47, 204 0x1.1073028d7234bp+0, 0x1.1500p-48, 205 0x1.11301d0125b5bp+0, 0x1.c000p-49, 206 0x1.11edbab5e2af9p+0, 0x1.6bc0p-46, 207 0x1.12abdc06c31d5p+0, 0x1.8400p-49, 208 0x1.136a814f2047dp+0, -0x1.ed00p-47, 209 0x1.1429aaea92de9p+0, 0x1.8e00p-49, 210 0x1.14e95934f3138p+0, 0x1.b400p-49, 211 0x1.15a98c8a58e71p+0, 0x1.5300p-47, 212 0x1.166a45471c3dfp+0, 0x1.3380p-47, 213 0x1.172b83c7d5211p+0, 0x1.8d40p-45, 214 0x1.17ed48695bb9fp+0, -0x1.5d00p-47, 215 0x1.18af9388c8d93p+0, -0x1.c880p-46, 216 0x1.1972658375d66p+0, 0x1.1f00p-46, 217 0x1.1a35beb6fcba7p+0, 0x1.0480p-46, 218 0x1.1af99f81387e3p+0, -0x1.7390p-43, 219 0x1.1bbe084045d54p+0, 0x1.4e40p-45, 220 0x1.1c82f95281c43p+0, -0x1.a200p-47, 221 0x1.1d4873168b9b2p+0, 0x1.3800p-49, 222 0x1.1e0e75eb44031p+0, 0x1.ac00p-49, 223 0x1.1ed5022fcd938p+0, 0x1.1900p-47, 224 0x1.1f9c18438cdf7p+0, -0x1.b780p-46, 225 0x1.2063b88628d8fp+0, 0x1.d940p-45, 226 0x1.212be3578a81ep+0, 0x1.8000p-50, 227 0x1.21f49917ddd41p+0, 0x1.b340p-45, 228 0x1.22bdda2791323p+0, 0x1.9f80p-46, 229 0x1.2387a6e7561e7p+0, -0x1.9c80p-46, 230 0x1.2451ffb821427p+0, 0x1.2300p-47, 231 0x1.251ce4fb2a602p+0, -0x1.3480p-46, 232 0x1.25e85711eceb0p+0, 0x1.2700p-46, 233 0x1.26b4565e27d16p+0, 0x1.1d00p-46, 234 0x1.2780e341de00fp+0, 0x1.1ee0p-44, 235 0x1.284dfe1f5633ep+0, -0x1.4c00p-46, 236 0x1.291ba7591bb30p+0, -0x1.3d80p-46, 237 0x1.29e9df51fdf09p+0, 0x1.8b00p-47, 238 0x1.2ab8a66d10e9bp+0, -0x1.27c0p-45, 239 0x1.2b87fd0dada3ap+0, 0x1.a340p-45, 240 0x1.2c57e39771af9p+0, -0x1.0800p-46, 241 0x1.2d285a6e402d9p+0, -0x1.ed00p-47, 242 0x1.2df961f641579p+0, -0x1.4200p-48, 243 0x1.2ecafa93e2ecfp+0, -0x1.4980p-45, 244 0x1.2f9d24abd8822p+0, -0x1.6300p-46, 245 0x1.306fe0a31b625p+0, -0x1.2360p-44, 246 0x1.31432edeea50bp+0, -0x1.0df8p-40, 247 0x1.32170fc4cd7b8p+0, -0x1.2480p-45, 248 0x1.32eb83ba8e9a2p+0, -0x1.5980p-45, 249 0x1.33c08b2641766p+0, 0x1.ed00p-46, 250 0x1.3496266e3fa27p+0, -0x1.c000p-50, 251 0x1.356c55f929f0fp+0, -0x1.0d80p-44, 252 0x1.36431a2de88b9p+0, 0x1.2c80p-45, 253 0x1.371a7373aaa39p+0, 0x1.0600p-45, 254 0x1.37f26231e74fep+0, -0x1.6600p-46, 255 0x1.38cae6d05d838p+0, -0x1.ae00p-47, 256 0x1.39a401b713ec3p+0, -0x1.4720p-43, 257 0x1.3a7db34e5a020p+0, 0x1.8200p-47, 258 0x1.3b57fbfec6e95p+0, 0x1.e800p-44, 259 0x1.3c32dc313a8f2p+0, 0x1.f800p-49, 260 0x1.3d0e544ede122p+0, -0x1.7a00p-46, 261 0x1.3dea64c1234bbp+0, 0x1.6300p-45, 262 0x1.3ec70df1c4eccp+0, -0x1.8a60p-43, 263 0x1.3fa4504ac7e8cp+0, -0x1.cdc0p-44, 264 0x1.40822c367a0bbp+0, 0x1.5b80p-45, 265 0x1.4160a21f72e95p+0, 0x1.ec00p-46, 266 0x1.423fb27094646p+0, -0x1.3600p-46, 267 0x1.431f5d950a920p+0, 0x1.3980p-45, 268 0x1.43ffa3f84b9ebp+0, 0x1.a000p-48, 269 0x1.44e0860618919p+0, -0x1.6c00p-48, 270 0x1.45c2042a7d201p+0, -0x1.bc00p-47, 271 0x1.46a41ed1d0016p+0, -0x1.2800p-46, 272 0x1.4786d668b3326p+0, 0x1.0e00p-44, 273 0x1.486a2b5c13c00p+0, -0x1.d400p-45, 274 0x1.494e1e192af04p+0, 0x1.c200p-47, 275 0x1.4a32af0d7d372p+0, -0x1.e500p-46, 276 0x1.4b17dea6db801p+0, 0x1.7800p-47, 277 0x1.4bfdad53629e1p+0, -0x1.3800p-46, 278 0x1.4ce41b817c132p+0, 0x1.0800p-47, 279 0x1.4dcb299fddddbp+0, 0x1.c700p-45, 280 0x1.4eb2d81d8ab96p+0, -0x1.ce00p-46, 281 0x1.4f9b2769d2d02p+0, 0x1.9200p-46, 282 0x1.508417f4531c1p+0, -0x1.8c00p-47, 283 0x1.516daa2cf662ap+0, -0x1.a000p-48, 284 0x1.5257de83f51eap+0, 0x1.a080p-43, 285 0x1.5342b569d4edap+0, -0x1.6d80p-45, 286 0x1.542e2f4f6ac1ap+0, -0x1.2440p-44, 287 0x1.551a4ca5d94dbp+0, 0x1.83c0p-43, 288 0x1.56070dde9116bp+0, 0x1.4b00p-45, 289 0x1.56f4736b529dep+0, 0x1.15a0p-43, 290 0x1.57e27dbe2c40ep+0, -0x1.9e00p-45, 291 0x1.58d12d497c76fp+0, -0x1.3080p-45, 292 0x1.59c0827ff0b4cp+0, 0x1.dec0p-43, 293 0x1.5ab07dd485427p+0, -0x1.4000p-51, 294 0x1.5ba11fba87af4p+0, 0x1.0080p-44, 295 0x1.5c9268a59460bp+0, -0x1.6c80p-45, 296 0x1.5d84590998e3fp+0, 0x1.69a0p-43, 297 0x1.5e76f15ad20e1p+0, -0x1.b400p-46, 298 0x1.5f6a320dcebcap+0, 0x1.7700p-46, 299 0x1.605e1b976dcb8p+0, 0x1.6f80p-45, 300 0x1.6152ae6cdf715p+0, 0x1.1000p-47, 301 0x1.6247eb03a5531p+0, -0x1.5d00p-46, 302 0x1.633dd1d1929b5p+0, -0x1.2d00p-46, 303 0x1.6434634ccc313p+0, -0x1.a800p-49, 304 0x1.652b9febc8efap+0, -0x1.8600p-45, 305 0x1.6623882553397p+0, 0x1.1fe0p-40, 306 0x1.671c1c708328ep+0, -0x1.7200p-44, 307 0x1.68155d44ca97ep+0, 0x1.6800p-49, 308 0x1.690f4b19e9471p+0, -0x1.9780p-45, 309 }; 310 311 /* 312 * exp2(x): compute the base 2 exponential of x 313 * 314 * Accuracy: Peak error < 0.503 ulp for normalized results. 315 * 316 * Method: (accurate tables) 317 * 318 * Reduce x: 319 * x = 2**k + y, for integer k and |y| <= 1/2. 320 * Thus we have exp2(x) = 2**k * exp2(y). 321 * 322 * Reduce y: 323 * y = i/TBLSIZE + z - eps[i] for integer i near y * TBLSIZE. 324 * Thus we have exp2(y) = exp2(i/TBLSIZE) * exp2(z - eps[i]), 325 * with |z - eps[i]| <= 2**-9 + 2**-39 for the table used. 326 * 327 * We compute exp2(i/TBLSIZE) via table lookup and exp2(z - eps[i]) via 328 * a degree-5 minimax polynomial with maximum error under 1.3 * 2**-61. 329 * The values in exp2t[] and eps[] are chosen such that 330 * exp2t[i] = exp2(i/TBLSIZE + eps[i]), and eps[i] is a small offset such 331 * that exp2t[i] is accurate to 2**-64. 332 * 333 * Note that the range of i is +-TBLSIZE/2, so we actually index the tables 334 * by i0 = i + TBLSIZE/2. For cache efficiency, exp2t[] and eps[] are 335 * virtual tables, interleaved in the real table tbl[]. 336 * 337 * This method is due to Gal, with many details due to Gal and Bachelis: 338 * 339 * Gal, S. and Bachelis, B. An Accurate Elementary Mathematical Library 340 * for the IEEE Floating Point Standard. TOMS 17(1), 26-46 (1991). 341 */ 342 double 343 exp2(double x) 344 { 345 double r, t, twopk, twopkp1000, z; 346 uint32_t hx, ix, lx, i0; 347 int k; 348 349 /* Filter out exceptional cases. */ 350 GET_HIGH_WORD(hx,x); 351 ix = hx & 0x7fffffff; /* high word of |x| */ 352 if(ix >= 0x40900000) { /* |x| >= 1024 */ 353 if(ix >= 0x7ff00000) { 354 GET_LOW_WORD(lx,x); 355 if(((ix & 0xfffff) | lx) != 0 || (hx & 0x80000000) == 0) 356 return (x + x); /* x is NaN or +Inf */ 357 else 358 return (0.0); /* x is -Inf */ 359 } 360 if(x >= 0x1.0p10) 361 return (huge * huge); /* overflow */ 362 if(x <= -0x1.0ccp10) 363 return (twom1000 * twom1000); /* underflow */ 364 } else if (ix < 0x3c900000) { /* |x| < 0x1p-54 */ 365 return (1.0 + x); 366 } 367 368 /* Reduce x, computing z, i0, and k. */ 369 STRICT_ASSIGN(double, t, x + redux); 370 GET_LOW_WORD(i0, t); 371 i0 += TBLSIZE / 2; 372 k = (i0 >> TBLBITS) << 20; 373 i0 = (i0 & (TBLSIZE - 1)) << 1; 374 t -= redux; 375 z = x - t; 376 377 /* Compute r = exp2(y) = exp2t[i0] * p(z - eps[i]). */ 378 t = tbl[i0]; /* exp2t[i0] */ 379 z -= tbl[i0 + 1]; /* eps[i0] */ 380 if (k >= -(1021 << 20)) 381 INSERT_WORDS(twopk, 0x3ff00000 + k, 0); 382 else 383 INSERT_WORDS(twopkp1000, 0x3ff00000 + k + (1000 << 20), 0); 384 r = t + t * z * (P1 + z * (P2 + z * (P3 + z * (P4 + z * P5)))); 385 386 /* Scale by 2**(k>>20). */ 387 if(k >= -(1021 << 20)) { 388 if (k == 1024 << 20) 389 return (r * 2.0 * 0x1p1023); 390 return (r * twopk); 391 } else { 392 return (r * twopkp1000 * twom1000); 393 } 394 }