android / platform / external / musl / 3ea3fcf78a5532e118856846df8adbf3f60ef716 / . / src / complex / __cexp.c

/* origin: FreeBSD /usr/src/lib/msun/src/k_exp.c */ | |

/*- | |

* Copyright (c) 2011 David Schultz <das@FreeBSD.ORG> | |

* All rights reserved. | |

* | |

* Redistribution and use in source and binary forms, with or without | |

* modification, are permitted provided that the following conditions | |

* are met: | |

* 1. Redistributions of source code must retain the above copyright | |

* notice, this list of conditions and the following disclaimer. | |

* 2. Redistributions in binary form must reproduce the above copyright | |

* notice, this list of conditions and the following disclaimer in the | |

* documentation and/or other materials provided with the distribution. | |

* | |

* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND | |

* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |

* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |

* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE | |

* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |

* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |

* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |

* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |

* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |

* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |

* SUCH DAMAGE. | |

*/ | |

#include "complex_impl.h" | |

static const uint32_t k = 1799; /* constant for reduction */ | |

static const double kln2 = 1246.97177782734161156; /* k * ln2 */ | |

/* | |

* Compute exp(x), scaled to avoid spurious overflow. An exponent is | |

* returned separately in 'expt'. | |

* | |

* Input: ln(DBL_MAX) <= x < ln(2 * DBL_MAX / DBL_MIN_DENORM) ~= 1454.91 | |

* Output: 2**1023 <= y < 2**1024 | |

*/ | |

static double __frexp_exp(double x, int *expt) | |

{ | |

double exp_x; | |

uint32_t hx; | |

/* | |

* We use exp(x) = exp(x - kln2) * 2**k, carefully chosen to | |

* minimize |exp(kln2) - 2**k|. We also scale the exponent of | |

* exp_x to MAX_EXP so that the result can be multiplied by | |

* a tiny number without losing accuracy due to denormalization. | |

*/ | |

exp_x = exp(x - kln2); | |

GET_HIGH_WORD(hx, exp_x); | |

*expt = (hx >> 20) - (0x3ff + 1023) + k; | |

SET_HIGH_WORD(exp_x, (hx & 0xfffff) | ((0x3ff + 1023) << 20)); | |

return exp_x; | |

} | |

/* | |

* __ldexp_cexp(x, expt) compute exp(x) * 2**expt. | |

* It is intended for large arguments (real part >= ln(DBL_MAX)) | |

* where care is needed to avoid overflow. | |

* | |

* The present implementation is narrowly tailored for our hyperbolic and | |

* exponential functions. We assume expt is small (0 or -1), and the caller | |

* has filtered out very large x, for which overflow would be inevitable. | |

*/ | |

double complex __ldexp_cexp(double complex z, int expt) | |

{ | |

double x, y, exp_x, scale1, scale2; | |

int ex_expt, half_expt; | |

x = creal(z); | |

y = cimag(z); | |

exp_x = __frexp_exp(x, &ex_expt); | |

expt += ex_expt; | |

/* | |

* Arrange so that scale1 * scale2 == 2**expt. We use this to | |

* compensate for scalbn being horrendously slow. | |

*/ | |

half_expt = expt / 2; | |

INSERT_WORDS(scale1, (0x3ff + half_expt) << 20, 0); | |

half_expt = expt - half_expt; | |

INSERT_WORDS(scale2, (0x3ff + half_expt) << 20, 0); | |

return CMPLX(cos(y) * exp_x * scale1 * scale2, sin(y) * exp_x * scale1 * scale2); | |

} |