modules/fdlibm/src/k_expf.cpp

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (c) 2011 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 "math_private.h"
  33
  34 static const uint32_t k = 235;                  /* constant for reduction */
  35 static const float kln2 =  162.88958740F;       /* k * ln2 */
  36
  37 /*
  38  * See k_exp.c for details.
  39  *
  40  * Input:  ln(FLT_MAX) <= x < ln(2 * FLT_MAX / FLT_MIN_DENORM) ~= 192.7
  41  * Output: 2**127 <= y < 2**128
  42  */
  43 static float
  44 __frexp_expf(float x, int *expt)
  45 {
  46         float exp_x;
  47         uint32_t hx;
  48
  49         exp_x = expf(x - kln2);
  50         GET_FLOAT_WORD(hx, exp_x);
  51         *expt = (hx >> 23) - (0x7f + 127) + k;
  52         SET_FLOAT_WORD(exp_x, (hx & 0x7fffff) | ((0x7f + 127) << 23));
  53         return (exp_x);
  54 }
  55
  56 float
  57 __ldexp_expf(float x, int expt)
  58 {
  59         float exp_x, scale;
  60         int ex_expt;
  61
  62         exp_x = __frexp_expf(x, &ex_expt);
  63         expt += ex_expt;
  64         SET_FLOAT_WORD(scale, (0x7f + expt) << 23);
  65         return (exp_x * scale);
  66 }