# HG changeset patch
# User Mike Miller <mtmiller@ieee.org>
# Date 1378657004 14400
# Node ID dbdff94bf9777ec588fadba4fd340dc7ce15538c
# Parent  e04847bbcfdfe6cf98301f06021b2310afded3eb
Use std::numeric_limits for floating point bit widths

* bitfcns.cc (max_mantissa_value<T>): New utility function.
(Fbitshift): Use max_mantissa_value, std::numeric_limits, and sizeof.
(Fbitmax): Use max_mantissa_value. Cast output properly for class single.

diff -r e04847bbcfdf -r dbdff94bf977 libinterp/corefcn/bitfcns.cc
--- a/libinterp/corefcn/bitfcns.cc	Sat Sep 07 12:21:38 2013 -0400
+++ b/libinterp/corefcn/bitfcns.cc	Sun Sep 08 12:16:44 2013 -0400
@@ -344,6 +344,13 @@
   return bitop ("bitxor", args);
 }
 
+template <typename T>
+static int64_t
+max_mantissa_value ()
+{
+  return (static_cast<int64_t> (1) << std::numeric_limits<T>::digits) - 1;
+}
+
 static int64_t
 bitshift (double a, int n, int64_t mask)
 {
@@ -543,13 +550,14 @@
         DO_SBITSHIFT (int64, nbits < 64 ? nbits : 64);
       else if (cname == "double")
         {
-          nbits = (nbits < 53 ? nbits : 53);
-          int64_t mask = 0x1FFFFFFFFFFFFFLL;
-          if (nbits < 53)
-            mask = mask >> (53 - nbits);
+          static const int bits_in_mantissa = std::numeric_limits<double>::digits;
+          nbits = (nbits < bits_in_mantissa ? nbits : bits_in_mantissa);
+          int64_t mask = max_mantissa_value<double> ();
+          if (nbits < bits_in_mantissa)
+            mask = mask >> (bits_in_mantissa - nbits);
           else if (nbits < 1)
             mask = 0;
-          int bits_in_type = 64;
+          int bits_in_type = sizeof (double) * CHAR_BIT;
           NDArray m = m_arg.array_value ();
           DO_BITSHIFT ( );
         }
@@ -592,9 +600,9 @@
     }
 
   if (cname == "double")
-    retval = (static_cast<double> (0x1FFFFFFFFFFFFFLL));
+    retval = (static_cast<double> (max_mantissa_value<double> ()));
   else if (cname == "single")
-    retval = (static_cast<double> (0xFFFFFFL));
+    retval = (static_cast<float> (max_mantissa_value<float> ()));
   else
     error ("bitmax: not defined for class '%s'", cname.c_str ());