github.com/afumu/libc@v0.0.6/musl/src/complex/__cexpf.c (about)

     1  /* origin: FreeBSD /usr/src/lib/msun/src/k_expf.c */
     2  /*-
     3   * Copyright (c) 2011 David Schultz <das@FreeBSD.ORG>
     4   * All rights reserved.
     5   *
     6   * Redistribution and use in source and binary forms, with or without
     7   * modification, are permitted provided that the following conditions
     8   * are met:
     9   * 1. Redistributions of source code must retain the above copyright
    10   *    notice, this list of conditions and the following disclaimer.
    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.
    14   *
    15   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
    16   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    17   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    18   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
    19   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    20   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
    21   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
    22   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    23   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
    24   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    25   * SUCH DAMAGE.
    26   */
    27  
    28  #include "complex_impl.h"
    29  
    30  static const uint32_t k = 235; /* constant for reduction */
    31  static const float kln2 = 162.88958740F; /* k * ln2 */
    32  
    33  /*
    34   * See __cexp.c for details.
    35   *
    36   * Input:  ln(FLT_MAX) <= x < ln(2 * FLT_MAX / FLT_MIN_DENORM) ~= 192.7
    37   * Output: 2**127 <= y < 2**128
    38   */
    39  static float __frexp_expf(float x, int *expt)
    40  {
    41  	float exp_x;
    42  	uint32_t hx;
    43  
    44  	exp_x = expf(x - kln2);
    45  	GET_FLOAT_WORD(hx, exp_x);
    46  	*expt = (hx >> 23) - (0x7f + 127) + k;
    47  	SET_FLOAT_WORD(exp_x, (hx & 0x7fffff) | ((0x7f + 127) << 23));
    48  	return exp_x;
    49  }
    50  
    51  float complex __ldexp_cexpf(float complex z, int expt)
    52  {
    53  	float x, y, exp_x, scale1, scale2;
    54  	int ex_expt, half_expt;
    55  
    56  	x = crealf(z);
    57  	y = cimagf(z);
    58  	exp_x = __frexp_expf(x, &ex_expt);
    59  	expt += ex_expt;
    60  
    61  	half_expt = expt / 2;
    62  	SET_FLOAT_WORD(scale1, (0x7f + half_expt) << 23);
    63  	half_expt = expt - half_expt;
    64  	SET_FLOAT_WORD(scale2, (0x7f + half_expt) << 23);
    65  
    66  	return CMPLXF(cosf(y) * exp_x * scale1 * scale2,
    67  	  sinf(y) * exp_x * scale1 * scale2);
    68  }