78 lines
2.0 KiB
C
78 lines
2.0 KiB
C
/* Support routines for the intrinsic power (**) operator.
|
|
Copyright (C) 2004-2017 Free Software Foundation, Inc.
|
|
Contributed by Paul Brook
|
|
|
|
This file is part of the GNU Fortran 95 runtime library (libgfortran).
|
|
|
|
Libgfortran is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 3 of the License, or (at your option) any later version.
|
|
|
|
Libgfortran is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
Under Section 7 of GPL version 3, you are granted additional
|
|
permissions described in the GCC Runtime Library Exception, version
|
|
3.1, as published by the Free Software Foundation.
|
|
|
|
You should have received a copy of the GNU General Public License and
|
|
a copy of the GCC Runtime Library Exception along with this program;
|
|
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#include "libgfortran.h"
|
|
|
|
|
|
/* Use Binary Method to calculate the powi. This is not an optimal but
|
|
a simple and reasonable arithmetic. See section 4.6.3, "Evaluation of
|
|
Powers" of Donald E. Knuth, "Seminumerical Algorithms", Vol. 2, "The Art
|
|
of Computer Programming", 3rd Edition, 1998. */
|
|
|
|
#if defined (HAVE_GFC_INTEGER_8) && defined (HAVE_GFC_INTEGER_16)
|
|
|
|
GFC_INTEGER_8 pow_i8_i16 (GFC_INTEGER_8 a, GFC_INTEGER_16 b);
|
|
export_proto(pow_i8_i16);
|
|
|
|
GFC_INTEGER_8
|
|
pow_i8_i16 (GFC_INTEGER_8 a, GFC_INTEGER_16 b)
|
|
{
|
|
GFC_INTEGER_8 pow, x;
|
|
GFC_INTEGER_16 n;
|
|
GFC_UINTEGER_16 u;
|
|
|
|
n = b;
|
|
x = a;
|
|
pow = 1;
|
|
if (n != 0)
|
|
{
|
|
if (n < 0)
|
|
{
|
|
if (x == 1)
|
|
return 1;
|
|
if (x == -1)
|
|
return (n & 1) ? -1 : 1;
|
|
return (x == 0) ? 1 / x : 0;
|
|
}
|
|
else
|
|
{
|
|
u = n;
|
|
}
|
|
for (;;)
|
|
{
|
|
if (u & 1)
|
|
pow *= x;
|
|
u >>= 1;
|
|
if (u)
|
|
x *= x;
|
|
else
|
|
break;
|
|
}
|
|
}
|
|
return pow;
|
|
}
|
|
|
|
#endif
|