diff --git a/src/comp/middle/trans.rs b/src/comp/middle/trans.rs
index a855fe2bacf7a..4c2abd17f36f4 100644
--- a/src/comp/middle/trans.rs
+++ b/src/comp/middle/trans.rs
@@ -1492,26 +1492,26 @@ tag scalar_type { nil_type; signed_int; unsigned_int; floating_point; }
 
 
 fn compare_scalar_types(cx: @block_ctxt, lhs: ValueRef, rhs: ValueRef,
-                        t: ty::t, llop: ValueRef) -> result {
-    let f = bind compare_scalar_values(cx, lhs, rhs, _, llop);
+                        t: ty::t, op: ast::binop) -> result {
+    let f = bind compare_scalar_values(cx, lhs, rhs, _, op);
 
     alt ty::struct(bcx_tcx(cx), t) {
-      ty::ty_nil. { ret f(nil_type); }
+      ty::ty_nil. { ret rslt(cx, f(nil_type)); }
       ty::ty_bool. | ty::ty_uint. | ty::ty_ptr(_) | ty::ty_char. {
-        ret f(unsigned_int);
+        ret rslt(cx, f(unsigned_int));
       }
-      ty::ty_int. { ret f(signed_int); }
-      ty::ty_float. { ret f(floating_point); }
+      ty::ty_int. { ret rslt(cx, f(signed_int)); }
+      ty::ty_float. { ret rslt(cx, f(floating_point)); }
       ty::ty_machine(_) {
         if ty::type_is_fp(bcx_tcx(cx), t) {
             // Floating point machine types
-            ret f(floating_point);
+            ret rslt(cx, f(floating_point));
         } else if ty::type_is_signed(bcx_tcx(cx), t) {
             // Signed, integral machine types
-            ret f(signed_int);
+            ret rslt(cx, f(signed_int));
         } else {
             // Unsigned, integral machine types
-            ret f(unsigned_int);
+            ret rslt(cx, f(unsigned_int));
         }
       }
       ty::ty_type. {
@@ -1535,70 +1535,50 @@ fn compare_scalar_types(cx: @block_ctxt, lhs: ValueRef, rhs: ValueRef,
 
 // A helper function to do the actual comparison of scalar values.
 fn compare_scalar_values(cx: @block_ctxt, lhs: ValueRef, rhs: ValueRef,
-                         nt: scalar_type, llop: ValueRef) -> result {
-    let eq_cmp;
-    let lt_cmp;
-    let le_cmp;
+                         nt: scalar_type, op: ast::binop) -> ValueRef {
     alt nt {
       nil_type. {
         // We don't need to do actual comparisons for nil.
         // () == () holds but () < () does not.
-        eq_cmp = 1u;
-        lt_cmp = 0u;
-        le_cmp = 1u;
+        alt op {
+          ast::eq. | ast::le. | ast::ge. { ret C_bool(true); }
+          ast::ne. | ast::lt. | ast::gt. { ret C_bool(false); }
+        }
       }
       floating_point. {
-        eq_cmp = lib::llvm::LLVMRealUEQ;
-        lt_cmp = lib::llvm::LLVMRealULT;
-        le_cmp = lib::llvm::LLVMRealULE;
+        let cmp = alt op {
+          ast::eq. { lib::llvm::LLVMRealOEQ }
+          ast::ne. { lib::llvm::LLVMRealUNE }
+          ast::lt. { lib::llvm::LLVMRealOLT }
+          ast::le. { lib::llvm::LLVMRealOLE }
+          ast::gt. { lib::llvm::LLVMRealOGT }
+          ast::ge. { lib::llvm::LLVMRealOGE }
+        };
+        ret FCmp(cx, cmp, lhs, rhs);
       }
       signed_int. {
-        eq_cmp = lib::llvm::LLVMIntEQ;
-        lt_cmp = lib::llvm::LLVMIntSLT;
-        le_cmp = lib::llvm::LLVMIntSLE;
+        let cmp = alt op {
+          ast::eq. { lib::llvm::LLVMIntEQ }
+          ast::ne. { lib::llvm::LLVMIntNE }
+          ast::lt. { lib::llvm::LLVMIntSLT }
+          ast::le. { lib::llvm::LLVMIntSLE }
+          ast::gt. { lib::llvm::LLVMIntSGT }
+          ast::ge. { lib::llvm::LLVMIntSGE }
+        };
+        ret ICmp(cx, cmp, lhs, rhs);
       }
       unsigned_int. {
-        eq_cmp = lib::llvm::LLVMIntEQ;
-        lt_cmp = lib::llvm::LLVMIntULT;
-        le_cmp = lib::llvm::LLVMIntULE;
-      }
-    }
-    // FIXME: This wouldn't be necessary if we could bind methods off of
-    // objects and therefore abstract over FCmp and ICmp (issue #435).  Then
-    // we could just write, e.g., "cmp_fn = bind FCmp(cx, _, _, _);" in
-    // the above, and "auto eq_result = cmp_fn(eq_cmp, lhs, rhs);" in the
-    // below.
-
-    fn generic_cmp(cx: @block_ctxt, nt: scalar_type, op: uint, lhs: ValueRef,
-                   rhs: ValueRef) -> ValueRef {
-        let r: ValueRef;
-        if nt == nil_type {
-            r = C_bool(op != 0u);
-        } else if nt == floating_point {
-            r = FCmp(cx, op, lhs, rhs);
-        } else { r = ICmp(cx, op, lhs, rhs); }
-        ret r;
-    }
-    let last_cx = new_sub_block_ctxt(cx, "last");
-    let eq_cx = new_sub_block_ctxt(cx, "eq");
-    let eq_result = generic_cmp(eq_cx, nt, eq_cmp, lhs, rhs);
-    Br(eq_cx, last_cx.llbb);
-    let lt_cx = new_sub_block_ctxt(cx, "lt");
-    let lt_result = generic_cmp(lt_cx, nt, lt_cmp, lhs, rhs);
-    Br(lt_cx, last_cx.llbb);
-    let le_cx = new_sub_block_ctxt(cx, "le");
-    let le_result = generic_cmp(le_cx, nt, le_cmp, lhs, rhs);
-    Br(le_cx, last_cx.llbb);
-    let unreach_cx = new_sub_block_ctxt(cx, "unreach");
-    Unreachable(unreach_cx);
-    let llswitch = Switch(cx, llop, unreach_cx.llbb, 3u);
-    AddCase(llswitch, C_u8(abi::cmp_glue_op_eq), eq_cx.llbb);
-    AddCase(llswitch, C_u8(abi::cmp_glue_op_lt), lt_cx.llbb);
-    AddCase(llswitch, C_u8(abi::cmp_glue_op_le), le_cx.llbb);
-    let last_result =
-        Phi(last_cx, T_i1(), [eq_result, lt_result, le_result],
-            [eq_cx.llbb, lt_cx.llbb, le_cx.llbb]);
-    ret rslt(last_cx, last_result);
+        let cmp = alt op {
+          ast::eq. { lib::llvm::LLVMIntEQ }
+          ast::ne. { lib::llvm::LLVMIntNE }
+          ast::lt. { lib::llvm::LLVMIntULT }
+          ast::le. { lib::llvm::LLVMIntULE }
+          ast::gt. { lib::llvm::LLVMIntUGT }
+          ast::ge. { lib::llvm::LLVMIntUGE }
+        };
+        ret ICmp(cx, cmp, lhs, rhs);
+      }
+    }
 }
 
 type val_pair_fn = fn(@block_ctxt, ValueRef, ValueRef) -> @block_ctxt;
@@ -1912,16 +1892,6 @@ fn call_cmp_glue(cx: @block_ctxt, lhs: ValueRef, rhs: ValueRef, t: ty::t,
     ret rslt(bcx, Load(bcx, llcmpresultptr));
 }
 
-// Compares two values. Performs the simple scalar comparison if the types are
-// scalar and calls to comparison glue otherwise.
-fn compare(cx: @block_ctxt, lhs: ValueRef, rhs: ValueRef, t: ty::t,
-           llop: ValueRef) -> result {
-    if ty::type_is_scalar(bcx_tcx(cx), t) {
-        ret compare_scalar_types(cx, lhs, rhs, t, llop);
-    }
-    ret call_cmp_glue(cx, lhs, rhs, t, llop);
-}
-
 fn take_ty(cx: @block_ctxt, v: ValueRef, t: ty::t) -> @block_ctxt {
     if ty::type_has_pointers(bcx_tcx(cx), t) {
         ret call_tydesc_glue(cx, v, t, abi::tydesc_field_take_glue);
@@ -2262,6 +2232,11 @@ fn trans_expr_fn(bcx: @block_ctxt, f: ast::_fn, sp: span,
 
 fn trans_compare(cx: @block_ctxt, op: ast::binop, lhs: ValueRef,
                  _lhs_t: ty::t, rhs: ValueRef, rhs_t: ty::t) -> result {
+    if ty::type_is_scalar(bcx_tcx(cx), rhs_t) {
+      let rs = compare_scalar_types(cx, lhs, rhs, rhs_t, op);
+      ret rslt(rs.bcx, rs.val);
+    }
+
     // Determine the operation we need.
     let llop;
     alt op {
@@ -2270,7 +2245,7 @@ fn trans_compare(cx: @block_ctxt, op: ast::binop, lhs: ValueRef,
       ast::le. | ast::gt. { llop = C_u8(abi::cmp_glue_op_le); }
     }
 
-    let rs = compare(cx, lhs, rhs, rhs_t, llop);
+    let rs = call_cmp_glue(cx, lhs, rhs, rhs_t, llop);
 
     // Invert the result if necessary.
     alt op {
diff --git a/src/lib/float.rs b/src/lib/float.rs
index 5bdf250069e94..c7053486ccb5a 100644
--- a/src/lib/float.rs
+++ b/src/lib/float.rs
@@ -213,13 +213,16 @@ fn NaN() -> float {
    ret 0./0.;
 }
 
+/* Predicate: isNaN */
+pure fn isNaN(f: float) -> bool { f != f }
+
 /* Function: infinity */
-fn infinity() -> float {
+pure fn infinity() -> float {
    ret 1./0.;
 }
 
 /* Function: neg_infinity */
-fn neg_infinity() -> float {
+pure fn neg_infinity() -> float {
    ret -1./0.;
 }
 
@@ -256,17 +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 */
-pure fn positive(x: float) -> bool { ret x > 0.; }
+/*
+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 */
-pure fn negative(x: float) -> bool { ret x < 0.; }
+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 x <= 0.; }
+/*
+Predicate: nonpositive
 
-/* Predicate: nonnegative */
-pure fn nonnegative(x: float) -> bool { ret x >= 0.; }
+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:
diff --git a/src/test/run-pass/float-nan.rs b/src/test/run-pass/float-nan.rs
new file mode 100644
index 0000000000000..d0ec3d4f9949c
--- /dev/null
+++ b/src/test/run-pass/float-nan.rs
@@ -0,0 +1,82 @@
+use std;
+import std::float;
+
+fn main() {
+  let nan = float::NaN();
+  assert(float::isNaN(nan));
+
+  let inf = float::infinity();
+  assert(-inf == float::neg_infinity());
+
+  assert( nan !=  nan);
+  assert( nan != -nan);
+  assert(-nan != -nan);
+  assert(-nan !=  nan);
+
+  assert( nan !=   1.);
+  assert( nan !=   0.);
+  assert( nan !=  inf);
+  assert( nan != -inf);
+
+  assert(  1. !=  nan);
+  assert(  0. !=  nan);
+  assert( inf !=  nan);
+  assert(-inf !=  nan);
+
+  assert(!( nan ==  nan));
+  assert(!( nan == -nan));
+  assert(!( nan ==   1.));
+  assert(!( nan ==   0.));
+  assert(!( nan ==  inf));
+  assert(!( nan == -inf));
+  assert(!(  1. ==  nan));
+  assert(!(  0. ==  nan));
+  assert(!( inf ==  nan));
+  assert(!(-inf ==  nan));
+  assert(!(-nan ==  nan));
+  assert(!(-nan == -nan));
+
+  assert(!( nan >  nan));
+  assert(!( nan > -nan));
+  assert(!( nan >   0.));
+  assert(!( nan >  inf));
+  assert(!( nan > -inf));
+  assert(!(  0. >  nan));
+  assert(!( inf >  nan));
+  assert(!(-inf >  nan));
+  assert(!(-nan >  nan));
+
+  assert(!(nan <   0.));
+  assert(!(nan <   1.));
+  assert(!(nan <  -1.));
+  assert(!(nan <  inf));
+  assert(!(nan < -inf));
+  assert(!(nan <  nan));
+  assert(!(nan < -nan));
+
+  assert(!(  0. < nan));
+  assert(!(  1. < nan));
+  assert(!( -1. < nan));
+  assert(!( inf < nan));
+  assert(!(-inf < nan));
+  assert(!(-nan < nan));
+
+  assert(float::isNaN(nan + inf));
+  assert(float::isNaN(nan + -inf));
+  assert(float::isNaN(nan + 0.));
+  assert(float::isNaN(nan + 1.));
+  assert(float::isNaN(nan * 1.));
+  assert(float::isNaN(nan / 1.));
+  assert(float::isNaN(nan / 0.));
+  assert(float::isNaN(0. / 0.));
+  assert(float::isNaN(-inf + inf));
+  assert(float::isNaN(inf - inf));
+
+  assert(!float::isNaN(-1.));
+  assert(!float::isNaN(0.));
+  assert(!float::isNaN(0.1));
+  assert(!float::isNaN(1.));
+  assert(!float::isNaN(inf));
+  assert(!float::isNaN(-inf));
+  assert(!float::isNaN(1./-inf));
+}
diff --git a/src/test/stdtest/float.rs b/src/test/stdtest/float.rs
index b77d83eb75735..d9de78b60090a 100644
--- a/src/test/stdtest/float.rs
+++ b/src/test/stdtest/float.rs
@@ -10,10 +10,53 @@ fn test_from_str() {
    assert ( float::from_str("2.5e10") == 25000000000. );
    assert ( float::from_str("25000000000.E-10") == 2.5 );
    assert ( float::from_str("") == 0. );
-   assert ( float::from_str("   ") == 0. );
+   assert ( float::isNaN(float::from_str("   ")) );
    assert ( float::from_str(".") == 0. );
    assert ( float::from_str("5.") == 5. );
    assert ( float::from_str(".5") == 0.5 );
    assert ( float::from_str("0.5") == 0.5 );
+}
+
+#[test]
+fn test_positive() {
+  assert(float::positive(float::infinity()));
+  assert(float::positive(1.));
+  assert(float::positive(0.));
+  assert(!float::positive(-1.));
+  assert(!float::positive(float::neg_infinity()));
+  assert(!float::positive(1./float::neg_infinity()));
+  assert(!float::positive(float::NaN()));
+}
 
+#[test]
+fn test_negative() {
+  assert(!float::negative(float::infinity()));
+  assert(!float::negative(1.));
+  assert(!float::negative(0.));
+  assert(float::negative(-1.));
+  assert(float::negative(float::neg_infinity()));
+  assert(float::negative(1./float::neg_infinity()));
+  assert(!float::negative(float::NaN()));
+}
+
+#[test]
+fn test_nonpositive() {
+  assert(!float::nonpositive(float::infinity()));
+  assert(!float::nonpositive(1.));
+  assert(!float::nonpositive(0.));
+  assert(float::nonpositive(-1.));
+  assert(float::nonpositive(float::neg_infinity()));
+  assert(float::nonpositive(1./float::neg_infinity()));
+  assert(!float::nonpositive(float::NaN()));
+}
+
+#[test]
+fn test_nonnegative() {
+  assert(float::nonnegative(float::infinity()));
+  assert(float::nonnegative(1.));
+  assert(float::nonnegative(0.));
+  assert(!float::nonnegative(-1.));
+  assert(!float::nonnegative(float::neg_infinity()));
+  assert(!float::nonnegative(1./float::neg_infinity()));
+  assert(!float::nonnegative(float::NaN()));
 }