auto merge of #11265 : c-a/rust/byteswap_from, r=alexcrichton

This patchset adds intrinsics similar to the to_[be|le][16|32|64] intrinsics but for going in the reverse direction, e.g. from big/little endian to host endian. Implementation wise they do exactly the same as the corresponding to_* functions but I think it anyway make sense to have them since using the to_* functions in the reverse direction is not entirely intuitive.

The first patch adds the intrinsics and the two following changes instances of bswap* to use the [to|from]_* intrinsics instead.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/libstd/unstable/intrinsics.rs b/src/libstd/unstable/intrinsics.rs
index 46dc03e82b0..e0089b599c5 100644
--- a/src/libstd/unstable/intrinsics.rs
+++ b/src/libstd/unstable/intrinsics.rs
@@ -500,6 +500,19 @@ extern "rust-intrinsic" {
 #[cfg(target_endian = "little")] pub fn to_be64(x: i64) -> i64 { unsafe { bswap64(x) } }
 #[cfg(target_endian = "big")]    pub fn to_be64(x: i64) -> i64 { x }
 
+#[cfg(target_endian = "little")] pub fn from_le16(x: i16) -> i16 { x }
+#[cfg(target_endian = "big")]    pub fn from_le16(x: i16) -> i16 { unsafe { bswap16(x) } }
+#[cfg(target_endian = "little")] pub fn from_le32(x: i32) -> i32 { x }
+#[cfg(target_endian = "big")]    pub fn from_le32(x: i32) -> i32 { unsafe { bswap32(x) } }
+#[cfg(target_endian = "little")] pub fn from_le64(x: i64) -> i64 { x }
+#[cfg(target_endian = "big")]    pub fn from_le64(x: i64) -> i64 { unsafe { bswap64(x) } }
+
+#[cfg(target_endian = "little")] pub fn from_be16(x: i16) -> i16 { unsafe { bswap16(x) } }
+#[cfg(target_endian = "big")]    pub fn from_be16(x: i16) -> i16 { x }
+#[cfg(target_endian = "little")] pub fn from_be32(x: i32) -> i32 { unsafe { bswap32(x) } }
+#[cfg(target_endian = "big")]    pub fn from_be32(x: i32) -> i32 { x }
+#[cfg(target_endian = "little")] pub fn from_be64(x: i64) -> i64 { unsafe { bswap64(x) } }
+#[cfg(target_endian = "big")]    pub fn from_be64(x: i64) -> i64 { x }
 
 /// `TypeId` represents a globally unique identifier for a type
 #[lang="type_id"] // This needs to be kept in lockstep with the code in trans/intrinsic.rs and