feature: support for floating-point rounding control.

* arith.c (flo_get_round_mode, flo_set_round_mode): New
functions.
(arith_init): Register global lexical variables flo-near,
flo-down, flo-up and flo-zero.
Register flo-get-round-mode and flo-set-round-mode intrinsic
functions.

* configure: Test for fesetround and fegetround variables,
and the associated constants, prpoducing a HAVE_ROUNDING_CTL_H
variable in config.h.

* txr.1: Documented new variables and functions.

1 files changed, 26 insertions, 0 deletions

diff --git a/configure b/configure
index 809c4553..f50b757f 100755
--- a/configure
+++ b/configure
@@ -1392,6 +1392,32 @@ if ! [ $have_dbl_decimal_dig ] ; then
 fi
 
 #
+# Rounding mode control.
+#
+
+printf "Checking for fesetround and fegetround ... "
+
+cat > conftest.c <<!
+#include <fenv.h>
+
+int main(void)
+{
+  int mode = fegetround();
+  fesetround(FE_TONEAREST);
+  fesetround(FE_DOWNWARD);
+  fesetround(FE_UPWARD);
+  fesetround(FE_TOWARDZERO);
+  return 0;
+}
+!
+if conftest ; then
+  printf "yes\n"
+  printf "#define HAVE_ROUNDING_CTL_H 1\n" >> config.h
+else
+  printf "no\n"
+fi
+
+#
 # Valgrind
 #