sdk/lib/crt/math/i386/ldexp.c

   1 /*
   2  * PROJECT:     ReactOS CRT
   3  * LICENSE:     LGPL-2.1-or-later (https://spdx.org/licenses/LGPL-2.1-or-later)
   4  * PURPOSE:     Implements the ldexp CRT function for IA-32 with Windows-compatible error codes.
   5  * COPYRIGHT:   Copyright 2010 Timo Kreuzer (timo.kreuzer@reactos.org)
   6  *              Copyright 2011 Pierre Schweitzer (pierre@reactos.org)
   7  *              Copyright 2019 Colin Finck (colin@reactos.org)
   8  */
   9
  10 #include <precomp.h>
  11
  12 double ldexp (double value, int exp)
  13 {
  14 #ifdef __GNUC__
  15     register double result;
  16 #endif
  17
  18     /* Check for value correctness
  19      * and set errno if required
  20      */
  21     if (_isnan(value))
  22     {
  23         errno = EDOM;
  24     }
  25
  26 #ifdef __GNUC__
  27     asm ("fscale"
  28          : "=t" (result)
  29          : "0" (value), "u" ((double)exp)
  30          : "1");
  31     return result;
  32 #else /* !__GNUC__ */
  33     __asm
  34     {
  35         fild exp
  36         fld value
  37         fscale
  38         fstp st(1)
  39     }
  40
  41     /* "fstp st(1)" has copied st(0) to st(1), then popped the FPU stack,
  42      * so that the value is again in st(0) now. Effectively, we have reduced
  43      * the FPU stack by one element while preserving st(0).
  44      * st(0) is also the register used for returning a double value. */
  45 #endif /* !__GNUC__ */
  46 }