x86_64: add fenv support from glibc

1 files changed, 44 insertions, 0 deletions

diff --git a/libm/x86_64/fesetround.c b/libm/x86_64/fesetround.c
new file mode 100644
index 000000000..312bddf85
--- /dev/null
+++ b/libm/x86_64/fesetround.c
@@ -0,0 +1,44 @@
+/* Set current rounding direction.
+   Copyright (C) 2001-2017 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <fenv.h>
+
+int
+fesetround (int round)
+{
+  unsigned short int cw;
+  int mxcsr;
+
+  if ((round & ~0xc00) != 0)
+    /* ROUND is no valid rounding mode.  */
+    return 1;
+
+  /* First set the x87 FPU.  */
+  __asm__ ("fnstcw %0" : "=m" (*&cw));
+  cw &= ~0xc00;
+  cw |= round;
+  __asm__ ("fldcw %0" : : "m" (*&cw));
+
+  /* And now the MSCSR register for SSE, the precision is at different bit
+     positions in the different units, we need to shift it 3 bits.  */
+  __asm__ ("stmxcsr %0" : "=m" (*&mxcsr));
+  mxcsr &= ~ 0x6000;
+  mxcsr |= round << 3;
+  __asm__ ("ldmxcsr %0" : : "m" (*&mxcsr));
+
+  return 0;
+}