* Makefile (conftest, conftest2): Link math

library so we can test for math functions.

* arith.c (log2_init): New static function.
(log2, logtwo): New functions.
(l2): New static variable.
(arith_init): Call log2_init.

* configure (lang_flags): Switching _XOPEN_SOURCE
from 500 to 600 to reveal log2.
Adding test for log2.

* eval.c (eval_init): Register log2 intrinsic.

* lib.h (logtwo): Declared.

* txr.1: Documented log2.

1 files changed, 19 insertions, 1 deletions

diff --git a/configure b/configure
index 16b84cd7..0d36cff6 100755
--- a/configure
+++ b/configure
@@ -97,7 +97,7 @@ yacc='$(cross)$(tool_prefix)$(yaccname)'
 yacc_given=
 nm='$(cross)$(tool_prefix)nm'
 opt_flags=-O2
-lang_flags='-ansi -D_XOPEN_SOURCE=500'
+lang_flags='-ansi -D_XOPEN_SOURCE=600'
 diag_flags='-Wall -Werror=implicit-function-declaration -Werror=missing-prototypes -Werror=strict-prototypes'
 debug_flags=-g
 inline=
@@ -1809,6 +1809,24 @@ else
   printf "no\n"
 fi
 
+printf "Checking for log2 ... "
+
+cat > conftest.c <<!
+#include <math.h>
+
+int main(void)
+{
+  double x = log2(42.0);
+  return 0;
+}
+!
+if conftest ; then
+  printf "yes\n"
+  printf "#define HAVE_LOG2 1\n" >> config.h
+else
+  printf "no\n"
+fi
+
 #
 # Dependent variables
 #