Change behavior of float::nonpositive/nonnegative

Rather than being defined as !positive and !negative, these should act the
same as negative and positive (respectively).  The only effect of this change
should be that all four functions will now return false for NaN.

src/lib/float.rs

@@ -259,17 +259,39 @@ pure fn ge(x: float, y: float) -> bool { ret x >= y; }
 /* Predicate: gt */
 pure fn gt(x: float, y: float) -> bool { ret x > y; }
 
-/* Predicate: positive */
+/*
+Predicate: positive
+
+Returns true if `x` is a positive number, including +0.0 and +Infinity.
+ */
 pure fn positive(x: float) -> bool { ret x > 0. || (1./x) == infinity(); }
 
-/* Predicate: negative */
+/*
+Predicate: negative
+
+Returns true if `x` is a negative number, including -0.0 and -Infinity.
+ */
 pure fn negative(x: float) -> bool { ret x < 0. || (1./x) == neg_infinity(); }
 
-/* Predicate: nonpositive */
-pure fn nonpositive(x: float) -> bool { ret !positive(x); }
+/*
+Predicate: nonpositive
 
-/* Predicate: nonnegative */
-pure fn nonnegative(x: float) -> bool { ret !negative(x); }
+Returns true if `x` is a negative number, including -0.0 and -Infinity.
+(This is the same as `float::negative`.)
+*/
+pure fn nonpositive(x: float) -> bool {
+  ret x < 0. || (1./x) == neg_infinity();
+}
+
+/*
+Predicate: nonnegative
+
+Returns true if `x` is a positive number, including +0.0 and +Infinity.
+(This is the same as `float::positive`.)
+*/
+pure fn nonnegative(x: float) -> bool {
+  ret x > 0. || (1./x) == infinity();
+}
 
 //
 // Local Variables:

src/test/stdtest/float.rs

@@ -47,7 +47,7 @@ fn test_nonpositive() {
   assert(float::nonpositive(-1.));
   assert(float::nonpositive(float::neg_infinity()));
   assert(float::nonpositive(1./float::neg_infinity()));
-  // TODO: assert(!float::nonpositive(float::NaN()));
+  assert(!float::nonpositive(float::NaN()));
 }
 
 #[test]
@@ -58,5 +58,5 @@ fn test_nonnegative() {
   assert(!float::nonnegative(-1.));
   assert(!float::nonnegative(float::neg_infinity()));
   assert(!float::nonnegative(1./float::neg_infinity()));
-  // TODO: assert(!float::nonnegative(float::NaN()));
+  assert(!float::nonnegative(float::NaN()));
 }