Auto merge of #26981 - wthrowe:div_docs, r=Gankro

This resolves #26845.

I'm not entirely satisfied with the placement of the rounding discussion in the docs for the `Div` and `Rem` traits, but I couldn't come up with anywhere better to put it.  Suggestions are welcome.

I didn't add any discussion of rounding to the `checked_div` (or rem) or `wrapping_div` documentation because those seem to make it pretty clear that they do the same thing as `Div`.

src/libcore/num/mod.rs

@@ -459,15 +459,15 @@ macro_rules! int_impl {
             }
         }
 
-        /// Wrapping (modular) division. Computes `floor(self / other)`,
+        /// Wrapping (modular) division. Computes `self / other`,
         /// wrapping around at the boundary of the type.
         ///
         /// The only case where such wrapping can occur is when one
         /// divides `MIN / -1` on a signed type (where `MIN` is the
         /// negative minimal value for the type); this is equivalent
         /// to `-MIN`, a positive value that is too large to represent
         /// in the type. In such a case, this function returns `MIN`
-        /// itself..
+        /// itself.
         #[stable(feature = "num_wrapping", since = "1.2.0")]
         #[inline(always)]
         pub fn wrapping_div(self, rhs: Self) -> Self {
@@ -1031,15 +1031,15 @@ macro_rules! uint_impl {
             }
         }
 
-        /// Wrapping (modular) division. Computes `floor(self / other)`,
+        /// Wrapping (modular) division. Computes `self / other`,
         /// wrapping around at the boundary of the type.
         ///
         /// The only case where such wrapping can occur is when one
         /// divides `MIN / -1` on a signed type (where `MIN` is the
         /// negative minimal value for the type); this is equivalent
         /// to `-MIN`, a positive value that is too large to represent
         /// in the type. In such a case, this function returns `MIN`
-        /// itself..
+        /// itself.
         #[stable(feature = "num_wrapping", since = "1.2.0")]
         #[inline(always)]
         pub fn wrapping_div(self, rhs: Self) -> Self {

src/libcore/ops.rs

@@ -351,8 +351,10 @@ pub trait Div<RHS=Self> {
     fn div(self, rhs: RHS) -> Self::Output;
 }
 
-macro_rules! div_impl {
+macro_rules! div_impl_integer {
     ($($t:ty)*) => ($(
+        /// This operation rounds towards zero, truncating any
+        /// fractional part of the exact result.
         #[stable(feature = "rust1", since = "1.0.0")]
         impl Div for $t {
             type Output = $t;
@@ -365,7 +367,23 @@ macro_rules! div_impl {
     )*)
 }
 
-div_impl! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64 }
+div_impl_integer! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 }
+
+macro_rules! div_impl_float {
+    ($($t:ty)*) => ($(
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl Div for $t {
+            type Output = $t;
+
+            #[inline]
+            fn div(self, other: $t) -> $t { self / other }
+        }
+
+        forward_ref_binop! { impl Div, div for $t, $t }
+    )*)
+}
+
+div_impl_float! { f32 f64 }
 
 /// The `Rem` trait is used to specify the functionality of `%`.
 ///
@@ -407,6 +425,8 @@ pub trait Rem<RHS=Self> {
 
 macro_rules! rem_impl {
     ($($t:ty)*) => ($(
+        /// This operation satisfies `n % d == n - (n / d) * d`.  The
+        /// result has the same sign as the left operand.
         #[stable(feature = "rust1", since = "1.0.0")]
         impl Rem for $t {
             type Output = $t;