1 /* Set current rounding direction.
2 Copyright (C) 2001-2017 Free Software Foundation, Inc.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <http://www.gnu.org/licenses/>. */
17
18 #include <fenv.h>
19
20 int
fesetround(int round)21 fesetround (int round)
22 {
23 unsigned short int cw;
24 int mxcsr;
25
26 if ((round & ~0xc00) != 0)
27 /* ROUND is no valid rounding mode. */
28 return 1;
29
30 /* First set the x87 FPU. */
31 __asm__ ("fnstcw %0" : "=m" (*&cw));
32 cw &= ~0xc00;
33 cw |= round;
34 __asm__ ("fldcw %0" : : "m" (*&cw));
35
36 /* And now the MSCSR register for SSE, the precision is at different bit
37 positions in the different units, we need to shift it 3 bits. */
38 __asm__ ("stmxcsr %0" : "=m" (*&mxcsr));
39 mxcsr &= ~ 0x6000;
40 mxcsr |= round << 3;
41 __asm__ ("ldmxcsr %0" : : "m" (*&mxcsr));
42
43 return 0;
44 }
45