comparesf2/comparedf2: fix a signedness bug and add tests.

library/compiler-builtins/src/float/cmp.rs

@@ -1,3 +1,5 @@
+#![allow(unreachable_code)]
+
 use int::{Int, CastInto};
 use float::Float;
 
@@ -35,18 +37,19 @@ fn cmp<F: Float>(a: F, b: F) -> Result where
     i32: CastInto<F::Int>,
     F::Int: CastInto<i32>,
 {
-    let one = F::Int::ONE;
-    let zero = F::Int::ZERO;
+    let one   = F::Int::ONE;
+    let zero  = F::Int::ZERO;
+    let szero = F::SignedInt::ZERO;
 
     let sign_bit =      F::SIGN_MASK as F::Int;
     let abs_mask =      sign_bit - one;
     let exponent_mask = F::EXPONENT_MASK;
     let inf_rep =       exponent_mask;
 
-    let a_rep = a.repr();
-    let b_rep = b.repr();
-    let a_abs = a_rep & abs_mask;
-    let b_abs = b_rep & abs_mask;
+    let a_rep  = a.repr();
+    let b_rep  = b.repr();
+    let a_abs  = a_rep & abs_mask;
+    let b_abs  = b_rep & abs_mask;
 
     // If either a or b is NaN, they are unordered.
     if a_abs > inf_rep || b_abs > inf_rep {
@@ -58,12 +61,15 @@ fn cmp<F: Float>(a: F, b: F) -> Result where
         return Result::Equal
     }
 
+    let a_srep = a.signed_repr();
+    let b_srep = b.signed_repr();
+
     // If at least one of a and b is positive, we get the same result comparing
     // a and b as signed integers as we would with a fp_ting-point compare.
-    if a_rep & b_rep >= zero {
-        if a_rep < b_rep {
+    if a_srep & b_srep >= szero {
+        if a_srep < b_srep {
             return Result::Less
-        } else if a_rep == b_rep {
+        } else if a_srep == b_srep {
             return Result::Equal
         } else {
             return Result::Greater
@@ -75,9 +81,9 @@ fn cmp<F: Float>(a: F, b: F) -> Result where
     // complement integer representation; if integers are represented in a
     // sign-magnitude representation, then this flip is incorrect).
     else {
-        if a_rep > b_rep {
+        if a_srep > b_srep {
             return Result::Less
-        } else if a_rep == b_rep {
+        } else if a_srep == b_srep {
             return Result::Equal
         } else {
             return Result::Greater

library/compiler-builtins/src/float/mod.rs

@@ -26,6 +26,9 @@ pub trait Float:
     /// A uint of the same with as the float
     type Int: Int;
 
+    /// A int of the same with as the float
+    type SignedInt: Int;
+
     const ZERO: Self;
     const ONE: Self;
 
@@ -59,6 +62,9 @@ pub trait Float:
     /// Returns `self` transmuted to `Self::Int`
     fn repr(self) -> Self::Int;
 
+    /// Returns `self` transmuted to `Self::SignedInt`
+    fn signed_repr(self) -> Self::SignedInt;
+
     #[cfg(test)]
     /// Checks if two floats have the same bit representation. *Except* for NaNs! NaN can be
     /// represented in multiple different ways. This method returns `true` if two NaNs are
@@ -78,9 +84,10 @@ pub trait Float:
 // FIXME: Some of this can be removed if RFC Issue #1424 is resolved
 //        https://github.com/rust-lang/rfcs/issues/1424
 macro_rules! float_impl {
-    ($ty:ident, $ity:ident, $bits:expr, $significand_bits:expr) => {
+    ($ty:ident, $ity:ident, $sity:ident, $bits:expr, $significand_bits:expr) => {
         impl Float for $ty {
             type Int = $ity;
+            type SignedInt = $sity;
             const ZERO: Self = 0.0;
             const ONE: Self = 1.0;
 
@@ -95,6 +102,9 @@ macro_rules! float_impl {
             fn repr(self) -> Self::Int {
                 unsafe { mem::transmute(self) }
             }
+            fn signed_repr(self) -> Self::SignedInt {
+                unsafe { mem::transmute(self) }
+            }
             #[cfg(test)]
             fn eq_repr(self, rhs: Self) -> bool {
                 if self.is_nan() && rhs.is_nan() {
@@ -120,5 +130,5 @@ macro_rules! float_impl {
     }
 }
 
-float_impl!(f32, u32, 32, 23);
-float_impl!(f64, u64, 64, 52);
+float_impl!(f32, u32, i32, 32, 23);
+float_impl!(f64, u64, i64, 64, 52);