Added negative cases for asinh according to IEEE-754.

Author: Phosphorus15

src/libstd/f32.rs

@@ -908,10 +908,17 @@ impl f32 {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asinh(self) -> f32 {
-        if self == NEG_INFINITY {
-            NEG_INFINITY
-        } else {
-            (self + ((self * self) + 1.0).sqrt()).ln()
+        match self {
+            x if x == NEG_INFINITY => NEG_INFINITY,
+            x if x.is_sign_negative() => {
+                let v = (x + ((x * x) + 1.0).sqrt()).ln();
+                if v.is_sign_negative() {
+                    v
+                } else {
+                    -v
+                }
+            }
+            x => (x + ((x * x) + 1.0).sqrt()).ln()
         }
     }
 

src/libstd/f64.rs

@@ -831,10 +831,17 @@ impl f64 {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asinh(self) -> f64 {
-        if self == NEG_INFINITY {
-            NEG_INFINITY
-        } else {
-            (self + ((self * self) + 1.0).sqrt()).ln()
+        match self {
+            x if x == NEG_INFINITY => NEG_INFINITY,
+            x if x.is_sign_negative() => {
+                let v = (x + ((x * x) + 1.0).sqrt()).ln();
+                if v.is_sign_negative() {
+                    v
+                } else {
+                    -v
+                }
+            }
+            x => (x + ((x * x) + 1.0).sqrt()).ln()
         }
     }