newlib/libm/common/nexttowardf.c

   1 /*
   2  * Copyright © 2005-2014 Rich Felker, et al.
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  18  * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
  19  * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  20  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  21  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 #include <math.h>
  25 #include <inttypes.h>
  26 #include "local.h"
  27
  28 union fshape {
  29   float value;
  30   uint32_t bits;
  31 };
  32
  33 // This is only necessary because the implementation of isnan only works
  34 // properly when long double == double.
  35 // See: https://sourceware.org/ml/newlib/2014/msg00684.html
  36 #ifdef _LDBL_EQ_DBL
  37
  38 float
  39 nexttowardf (float x, long double y)
  40 {
  41   union fshape ux;
  42   uint32_t e;
  43
  44   if (isnan(x) || isnan(y))
  45     return x + y;
  46   if (x == y)
  47     return y;
  48   ux.value = x;
  49   if (x == 0) {
  50     ux.bits = 1;
  51     if (signbit(y))
  52       ux.bits |= 0x80000000;
  53   } else if (x < y) {
  54     if (signbit(x))
  55       ux.bits--;
  56     else
  57       ux.bits++;
  58   } else {
  59     if (signbit(x))
  60       ux.bits++;
  61     else
  62       ux.bits--;
  63   }
  64   e = ux.bits & 0x7f800000;
  65   /* raise overflow if ux.value is infinite and x is finite */
  66   if (e == 0x7f800000) {
  67     volatile float force_eval;
  68     force_eval = x + x;
  69   }
  70   /* raise underflow if ux.value is subnormal or zero */
  71   if (e == 0) {
  72     volatile float force_eval;
  73     force_eval = x*x + ux.value*ux.value;
  74   }
  75   return ux.value;
  76 }
  77
  78 #endif // _LDBL_EQ_DBL