Move the CompactTarget type to primitives

Potentially the whole `pow` module will move to `primitives` but this
is not possible easily right now. However, we would like to be able to
move the `BlockHash` and `block::Header` types over to `primitives`
and doing so requires the `CompactTarget` to be there.

Move the `CompactTarget` type to `primitives` and re-export it from the
`primitives` crate root.

Note also, we re-export the type publicly from `bitcoin::pow`.

bitcoin/src/pow.rs

@@ -18,6 +18,10 @@ use crate::consensus::encode::{self, Decodable, Encodable};
 use crate::internal_macros::define_extension_trait;
 use crate::network::Params;
 
+#[rustfmt::skip]                // Keep public re-exports separate.
+#[doc(inline)]
+pub use primitives::CompactTarget;
+
 /// Implement traits and methods shared by `Target` and `Work`.
 macro_rules! do_impl {
     ($ty:ident) => {
@@ -330,32 +334,6 @@ impl Target {
 }
 do_impl!(Target);
 
-/// Encoding of 256-bit target as 32-bit float.
-///
-/// This is used to encode a target into the block header. Satoshi made this part of consensus code
-/// in the original version of Bitcoin, likely copying an idea from OpenSSL.
-///
-/// OpenSSL's bignum (BN) type has an encoding, which is even called "compact" as in bitcoin, which
-/// is exactly this format.
-///
-/// # Note on order/equality
-///
-/// Usage of the ordering and equality traits for this type may be surprising. Converting between
-/// `CompactTarget` and `Target` is lossy *in both directions* (there are multiple `CompactTarget`
-/// values that map to the same `Target` value). Ordering and equality for this type are defined in
-/// terms of the underlying `u32`.
-#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
-#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-pub struct CompactTarget(u32);
-
-impl CompactTarget {
-    /// Creates a [`CompactTarget`] from a consensus encoded `u32`.
-    pub fn from_consensus(bits: u32) -> Self { Self(bits) }
-
-    /// Returns the consensus encoded `u32` representation of this [`CompactTarget`].
-    pub fn to_consensus(self) -> u32 { self.0 }
-}
-
 define_extension_trait! {
     /// Extension functionality for the [`CompactTarget`] type.
     pub trait CompactTargetExt impl for CompactTarget {
@@ -467,16 +445,6 @@ impl Decodable for CompactTarget {
     }
 }
 
-impl fmt::LowerHex for CompactTarget {
-    #[inline]
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(&self.0, f) }
-}
-
-impl fmt::UpperHex for CompactTarget {
-    #[inline]
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::UpperHex::fmt(&self.0, f) }
-}
-
 /// Big-endian 256 bit integer type.
 // (high, low): u.0 contains the high bits, u.1 contains the low bits.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]

primitives/src/lib.rs

@@ -31,6 +31,7 @@ extern crate serde;
 #[cfg(feature = "alloc")]
 pub mod locktime;
 pub mod opcodes;
+pub mod pow;
 pub mod sequence;
 
 #[doc(inline)]
@@ -40,7 +41,10 @@ pub use units::*;
 #[cfg(feature = "alloc")]
 pub use self::locktime::{absolute, relative};
 #[doc(inline)]
-pub use self::sequence::Sequence;
+pub use self::{
+    pow::CompactTarget,
+    sequence::Sequence,
+};
 
 #[rustfmt::skip]
 #[allow(unused_imports)]

primitives/src/pow.rs

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: CC0-1.0
+
+//! Proof-of-work related integer types.
+
+use core::fmt;
+
+/// Encoding of 256-bit target as 32-bit float.
+///
+/// This is used to encode a target into the block header. Satoshi made this part of consensus code
+/// in the original version of Bitcoin, likely copying an idea from OpenSSL.
+///
+/// OpenSSL's bignum (BN) type has an encoding, which is even called "compact" as in bitcoin, which
+/// is exactly this format.
+///
+/// # Note on order/equality
+///
+/// Usage of the ordering and equality traits for this type may be surprising. Converting between
+/// `CompactTarget` and `Target` is lossy *in both directions* (there are multiple `CompactTarget`
+/// values that map to the same `Target` value). Ordering and equality for this type are defined in
+/// terms of the underlying `u32`.
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct CompactTarget(u32);
+
+impl CompactTarget {
+    /// Creates a [`CompactTarget`] from a consensus encoded `u32`.
+    pub fn from_consensus(bits: u32) -> Self { Self(bits) }
+
+    /// Returns the consensus encoded `u32` representation of this [`CompactTarget`].
+    pub fn to_consensus(self) -> u32 { self.0 }
+}
+
+impl fmt::LowerHex for CompactTarget {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(&self.0, f) }
+}
+
+impl fmt::UpperHex for CompactTarget {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::UpperHex::fmt(&self.0, f) }
+}