Merge branch 'v0.4.x' into uplift-0.4-commits

src/bytes.rs

@@ -273,7 +273,7 @@ pub struct BytesMut {
 // The rest of `arc`'s bytes are used as part of the inline buffer, which means
 // that those bytes need to be located next to the `ptr`, `len`, and `cap`
 // fields, which make up the rest of the inline buffer. This requires special
-// casing the layout of `Inner` depending on if the target platform is bit or
+// casing the layout of `Inner` depending on if the target platform is big or
 // little endian.
 //
 // On little endian platforms, the `arc` field must be the first field in the
@@ -590,6 +590,46 @@ impl Bytes {
         self.slice(0, end)
     }
 
+    /// Returns a slice of self that is equivalent to the given `subset`.
+    ///
+    /// When processing a `Bytes` buffer with other tools, one often gets a
+    /// `&[u8]` which is in fact a slice of the `Bytes`, i.e. a subset of it.
+    /// This function turns that `&[u8]` into another `Bytes`, as if one had
+    /// called `self.slice()` with the offsets that correspond to `subset`.
+    ///
+    /// This operation is `O(1)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let bytes = Bytes::from(&b"012345678"[..]);
+    /// let as_slice = bytes.as_ref();
+    /// let subset = &as_slice[2..6];
+    /// let subslice = bytes.slice_ref(&subset);
+    /// assert_eq!(&subslice[..], b"2345");
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Requires that the given `sub` slice is in fact contained within the
+    /// `Bytes` buffer; otherwise this function will panic.
+    pub fn slice_ref(&self, subset: &[u8]) -> Bytes {
+        let bytes_p = self.as_ptr() as usize;
+        let bytes_len = self.len();
+
+        let sub_p = subset.as_ptr() as usize;
+        let sub_len = subset.len();
+
+        assert!(sub_p >= bytes_p);
+        assert!(sub_p + sub_len <= bytes_p + bytes_len);
+
+        let sub_offset = sub_p - bytes_p;
+
+        self.slice(sub_offset, sub_offset + sub_len)
+    }
+
     /// Splits the bytes into two at the given index.
     ///
     /// Afterwards `self` contains elements `[0, at)`, and the returned `Bytes`
@@ -946,6 +986,18 @@ impl FromIterator<u8> for Bytes {
     }
 }
 
+impl<'a> FromIterator<&'a u8> for BytesMut {
+    fn from_iter<T: IntoIterator<Item = &'a u8>>(into_iter: T) -> Self {
+        BytesMut::from_iter(into_iter.into_iter().map(|b| *b))
+    }
+}
+
+impl<'a> FromIterator<&'a u8> for Bytes {
+    fn from_iter<T: IntoIterator<Item = &'a u8>>(into_iter: T) -> Self {
+        BytesMut::from_iter(into_iter).freeze()
+    }
+}
+
 impl PartialEq for Bytes {
     fn eq(&self, other: &Bytes) -> bool {
         self.inner.as_ref() == other.inner.as_ref()
@@ -1287,6 +1339,8 @@ impl BytesMut {
     ///
     /// Panics if `at > len`.
     pub fn split_to(&mut self, at: usize) -> BytesMut {
+        assert!(at <= self.len());
+
         BytesMut {
             inner: self.inner.split_to(at),
         }
@@ -2474,6 +2528,10 @@ impl Inner {
         // bits, so even without any explicit atomic operations, reading the
         // flag will be correct.
         //
+        // This is undefind behavior due to a data race, but experimental
+        // evidence shows that it works in practice (discussion:
+        // https://internals.rust-lang.org/t/bit-wise-reasoning-for-atomic-accesses/8853).
+        //
         // This function is very critical performance wise as it is called for
         // every operation. Performing an atomic load would mess with the
         // compiler's ability to optimize. Simple benchmarks show up to a 10%
@@ -2483,7 +2541,7 @@ impl Inner {
         #[inline]
         fn imp(arc: &AtomicPtr<Shared>) -> usize {
             unsafe {
-                let p: &u8 = mem::transmute(arc);
+                let p: *const u8 = mem::transmute(arc);
                 (*p as usize) & KIND_MASK
             }
         }
@@ -2492,7 +2550,7 @@ impl Inner {
         #[inline]
         fn imp(arc: &AtomicPtr<Shared>) -> usize {
             unsafe {
-                let p: &usize = mem::transmute(arc);
+                let p: *const usize = mem::transmute(arc);
                 *p & KIND_MASK
             }
         }
@@ -2508,7 +2566,7 @@ impl Inner {
         // function.
         let prev = unsafe {
             let p: &AtomicPtr<Shared> = &self.arc;
-            let p: &usize = mem::transmute(p);
+            let p: *const usize = mem::transmute(p);
             *p
         };
 
@@ -2615,35 +2673,51 @@ fn original_capacity_from_repr(repr: usize) -> usize {
 
 #[test]
 fn test_original_capacity_to_repr() {
-    for &cap in &[0, 1, 16, 1000] {
-        assert_eq!(0, original_capacity_to_repr(cap));
-    }
+    assert_eq!(original_capacity_to_repr(0), 0);
 
-    for &cap in &[1024, 1025, 1100, 2000, 2047] {
-        assert_eq!(1, original_capacity_to_repr(cap));
-    }
+    let max_width = 32;
 
-    for &cap in &[2048, 2049] {
-        assert_eq!(2, original_capacity_to_repr(cap));
-    }
+    for width in 1..(max_width + 1) {
+        let cap = 1 << width - 1;
 
-    // TODO: more
+        let expected = if width < MIN_ORIGINAL_CAPACITY_WIDTH {
+            0
+        } else if width < MAX_ORIGINAL_CAPACITY_WIDTH {
+            width - MIN_ORIGINAL_CAPACITY_WIDTH
+        } else {
+            MAX_ORIGINAL_CAPACITY_WIDTH - MIN_ORIGINAL_CAPACITY_WIDTH
+        };
 
-    for &cap in &[65536, 65537, 68000, 1 << 17, 1 << 18, 1 << 20, 1 << 30] {
-        assert_eq!(7, original_capacity_to_repr(cap), "cap={}", cap);
+        assert_eq!(original_capacity_to_repr(cap), expected);
+
+        if width > 1 {
+            assert_eq!(original_capacity_to_repr(cap + 1), expected);
+        }
+
+        //  MIN_ORIGINAL_CAPACITY_WIDTH must be bigger than 7 to pass tests below
+        if width == MIN_ORIGINAL_CAPACITY_WIDTH + 1 {
+            assert_eq!(original_capacity_to_repr(cap - 24), expected - 1);
+            assert_eq!(original_capacity_to_repr(cap + 76), expected);
+        } else if width == MIN_ORIGINAL_CAPACITY_WIDTH + 2 {
+            assert_eq!(original_capacity_to_repr(cap - 1), expected - 1);
+            assert_eq!(original_capacity_to_repr(cap - 48), expected - 1);
+        }
     }
 }
 
 #[test]
 fn test_original_capacity_from_repr() {
     assert_eq!(0, original_capacity_from_repr(0));
-    assert_eq!(1024, original_capacity_from_repr(1));
-    assert_eq!(1024 * 2, original_capacity_from_repr(2));
-    assert_eq!(1024 * 4, original_capacity_from_repr(3));
-    assert_eq!(1024 * 8, original_capacity_from_repr(4));
-    assert_eq!(1024 * 16, original_capacity_from_repr(5));
-    assert_eq!(1024 * 32, original_capacity_from_repr(6));
-    assert_eq!(1024 * 64, original_capacity_from_repr(7));
+
+    let min_cap = 1 << MIN_ORIGINAL_CAPACITY_WIDTH;
+
+    assert_eq!(min_cap, original_capacity_from_repr(1));
+    assert_eq!(min_cap * 2, original_capacity_from_repr(2));
+    assert_eq!(min_cap * 4, original_capacity_from_repr(3));
+    assert_eq!(min_cap * 8, original_capacity_from_repr(4));
+    assert_eq!(min_cap * 16, original_capacity_from_repr(5));
+    assert_eq!(min_cap * 32, original_capacity_from_repr(6));
+    assert_eq!(min_cap * 64, original_capacity_from_repr(7));
 }
 
 unsafe impl Send for Inner {}