| /* |
| * Copyright (c) 2014 Advanced Micro Devices, Inc. |
| * |
| * Permission is hereby granted, free of charge, to any person obtaining a copy |
| * of this software and associated documentation files (the "Software"), to deal |
| * in the Software without restriction, including without limitation the rights |
| * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell |
| * copies of the Software, and to permit persons to whom the Software is |
| * furnished to do so, subject to the following conditions: |
| * |
| * The above copyright notice and this permission notice shall be included in |
| * all copies or substantial portions of the Software. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
| * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
| * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE |
| * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
| * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, |
| * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN |
| * THE SOFTWARE. |
| */ |
| |
| #include "math64.h" |
| |
| __attribute__((overloadable)) double |
| atan(double x) |
| { |
| const double piby2 = 1.5707963267948966e+00; // 0x3ff921fb54442d18 |
| |
| double v = fabs(x); |
| |
| // 2^56 > v > 39/16 |
| double a = -1.0; |
| double b = v; |
| // (chi + clo) = arctan(infinity) |
| double chi = 1.57079632679489655800e+00; |
| double clo = 6.12323399573676480327e-17; |
| |
| double ta = v - 1.5; |
| double tb = 1.0 + 1.5 * v; |
| int l = v <= 0x1.38p+1; // 39/16 > v > 19/16 |
| a = l ? ta : a; |
| b = l ? tb : b; |
| // (chi + clo) = arctan(1.5) |
| chi = l ? 9.82793723247329054082e-01 : chi; |
| clo = l ? 1.39033110312309953701e-17 : clo; |
| |
| ta = v - 1.0; |
| tb = 1.0 + v; |
| l = v <= 0x1.3p+0; // 19/16 > v > 11/16 |
| a = l ? ta : a; |
| b = l ? tb : b; |
| // (chi + clo) = arctan(1.) |
| chi = l ? 7.85398163397448278999e-01 : chi; |
| clo = l ? 3.06161699786838240164e-17 : clo; |
| |
| ta = 2.0 * v - 1.0; |
| tb = 2.0 + v; |
| l = v <= 0x1.6p-1; // 11/16 > v > 7/16 |
| a = l ? ta : a; |
| b = l ? tb : b; |
| // (chi + clo) = arctan(0.5) |
| chi = l ? 4.63647609000806093515e-01 : chi; |
| clo = l ? 2.26987774529616809294e-17 : clo; |
| |
| l = v <= 0x1.cp-2; // v < 7/16 |
| a = l ? v : a; |
| b = l ? 1.0 : b;; |
| chi = l ? 0.0 : chi; |
| clo = l ? 0.0 : clo; |
| |
| // Core approximation: Remez(4,4) on [-7/16,7/16] |
| double r = a / b; |
| double s = r * r; |
| double qn = fma(s, |
| fma(s, |
| fma(s, |
| fma(s, 0.142316903342317766e-3, |
| 0.304455919504853031e-1), |
| 0.220638780716667420e0), |
| 0.447677206805497472e0), |
| 0.268297920532545909e0); |
| |
| double qd = fma(s, |
| fma(s, |
| fma(s, |
| fma(s, 0.389525873944742195e-1, |
| 0.424602594203847109e0), |
| 0.141254259931958921e1), |
| 0.182596787737507063e1), |
| 0.804893761597637733e0); |
| |
| double q = r * s * qn / qd; |
| r = chi - ((q - clo) - r); |
| |
| double z = isnan(x) ? x : piby2; |
| z = v <= 0x1.0p+56 ? r : z; |
| z = v < 0x1.0p-26 ? v : z; |
| return x == v ? z : -z; |
| } |
| |