Add segwit version field element consts

Add two field element consts for segwit version 0 an version 1. This
makes reading the code much easier since one does not have to remember p
ad q.

Author: tcharding

src/primitives/decode.rs

@@ -35,6 +35,7 @@
 //! ```
 //! use bech32::{Bech32, Bech32m, Fe32, Hrp};
 //! use bech32::primitives::decode::{CheckedHrpstring, SegwitHrpstring, UncheckedHrpstring};
+//! use bech32::segwit::VERSION_1;
 //!
 //! // An arbitrary HRP and a string of valid bech32 characters.
 //! let s = "abcd143hj65vxw49rts6kcw35u6r6tgzguyr03vvveeewjqpn05efzq444444";
@@ -66,7 +67,7 @@
 //! let segwit = SegwitHrpstring::new(address).expect("valid segwit address");
 //! let _encoded_data = segwit.byte_iter();
 //! assert_eq!(segwit.hrp(), Hrp::parse("bc").unwrap());
-//! assert_eq!(segwit.witness_version(), Fe32::P);
+//! assert_eq!(segwit.witness_version(), VERSION_1);
 //! ```
 //!
 //! [BIP-173]: <https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki>
@@ -78,7 +79,7 @@ use crate::primitives::checksum::{self, Checksum};
 use crate::primitives::gf32::Fe32;
 use crate::primitives::hrp::{self, Hrp};
 use crate::primitives::iter::{Fe32IterExt, FesToBytes};
-use crate::primitives::segwit::{self, WitnessLengthError};
+use crate::primitives::segwit::{self, WitnessLengthError, VERSION_0};
 use crate::{write_err, Bech32, Bech32m};
 
 /// Separator between the hrp and payload (as defined by BIP-173).
@@ -363,7 +364,7 @@ impl<'s> SegwitHrpstring<'s> {
         }
 
         let checked: CheckedHrpstring<'s> = match witness_version {
-            Fe32::Q => unchecked.validate_and_remove_checksum::<Bech32>()?,
+            VERSION_0 => unchecked.validate_and_remove_checksum::<Bech32>()?,
             _ => unchecked.validate_and_remove_checksum::<Bech32m>()?,
         };
 

src/primitives/segwit.rs

@@ -9,6 +9,11 @@ use core::fmt;
 
 use crate::primitives::gf32::Fe32;
 
+/// The field element representing segwit version 0.
+pub const VERSION_0: Fe32 = Fe32::Q;
+/// The field element representing segwit version 1 (taproot).
+pub const VERSION_1: Fe32 = Fe32::P;
+
 /// Returns true if given field element represents a valid segwit version.
 pub fn is_valid_witness_version(witness_version: Fe32) -> bool {
     validate_witness_version(witness_version).is_ok()
@@ -41,7 +46,7 @@ pub fn validate_witness_program_length(
     if length > 40 {
         return Err(TooLong);
     }
-    if version == Fe32::Q && length != 20 && length != 32 {
+    if version == VERSION_0 && length != 20 && length != 32 {
         return Err(InvalidSegwitV0);
     }
     Ok(())

src/segwit.rs

@@ -27,7 +27,7 @@
 //! let _ = segwit::encode_v0(&hrp::TB, &witness_prog);
 //!
 //! // If you have the witness version already you can use:
-//! # let witness_version = Fe32::Q;
+//! # let witness_version = segwit::VERSION_0;
 //! let _ = segwit::encode(&hrp::BC, witness_version, &witness_prog);
 //!
 //! // Decode a Bitcoin bech32 segwit address.
@@ -50,9 +50,8 @@ use crate::primitives::decode::{SegwitHrpstring, SegwitHrpstringError};
 use crate::primitives::gf32::Fe32;
 use crate::primitives::hrp::Hrp;
 use crate::primitives::iter::{ByteIterExt, Fe32IterExt};
-#[cfg(feature = "alloc")]
-use crate::primitives::segwit;
-use crate::primitives::segwit::{InvalidWitnessVersionError, WitnessLengthError};
+use crate::primitives::segwit::{self, InvalidWitnessVersionError, WitnessLengthError};
+pub use crate::primitives::segwit::{VERSION_0, VERSION_1};
 use crate::primitives::{Bech32, Bech32m};
 use crate::write_err;
 
@@ -102,13 +101,13 @@ pub fn encode(
 /// Encodes a segwit version 0 address.
 #[cfg(feature = "alloc")]
 pub fn encode_v0(hrp: &Hrp, witness_program: &[u8]) -> Result<String, EncodeError> {
-    encode(hrp, Fe32::Q, witness_program)
+    encode(hrp, VERSION_0, witness_program)
 }
 
 /// Encodes a segwit version 1 address.
 #[cfg(feature = "alloc")]
 pub fn encode_v1(hrp: &Hrp, witness_program: &[u8]) -> Result<String, EncodeError> {
-    encode(hrp, Fe32::P, witness_program)
+    encode(hrp, VERSION_1, witness_program)
 }
 
 /// Encodes a segwit address to a writer ([`fmt::Write`]) using lowercase characters.
@@ -123,8 +122,8 @@ pub fn encode_to_fmt_unchecked<W: fmt::Write>(
 ) -> fmt::Result {
     let iter = witness_program.iter().copied().bytes_to_fes();
     match witness_version {
-        Fe32::Q => {
-            for c in iter.with_checksum::<Bech32>(hrp).with_witness_version(Fe32::Q).chars() {
+        VERSION_0 => {
+            for c in iter.with_checksum::<Bech32>(hrp).with_witness_version(VERSION_0).chars() {
                 fmt.write_char(c)?;
             }
         }
@@ -151,8 +150,8 @@ pub fn encode_to_fmt_unchecked_uppercase<W: fmt::Write>(
 ) -> fmt::Result {
     let iter = witness_program.iter().copied().bytes_to_fes();
     match witness_version {
-        Fe32::Q => {
-            for c in iter.with_checksum::<Bech32>(hrp).with_witness_version(Fe32::Q).chars() {
+        VERSION_0 => {
+            for c in iter.with_checksum::<Bech32>(hrp).with_witness_version(VERSION_0).chars() {
                 fmt.write_char(c.to_ascii_uppercase())?;
             }
         }
@@ -247,7 +246,7 @@ mod tests {
     fn encode_to_fmt_lowercase() {
         let program = witness_program();
         let mut address = String::new();
-        encode_to_fmt_unchecked(&mut address, &hrp::BC, Fe32::Q, &program)
+        encode_to_fmt_unchecked(&mut address, &hrp::BC, VERSION_0, &program)
             .expect("failed to encode address to QR code");
 
         let want = "bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4";
@@ -258,7 +257,7 @@ mod tests {
     fn encode_to_fmt_uppercase() {
         let program = witness_program();
         let mut address = String::new();
-        encode_to_fmt_unchecked_uppercase(&mut address, &hrp::BC, Fe32::Q, &program)
+        encode_to_fmt_unchecked_uppercase(&mut address, &hrp::BC, VERSION_0, &program)
             .expect("failed to encode address to QR code");
 
         let want = "BC1QW508D6QEJXTDG4Y5R3ZARVARY0C5XW7KV8F3T4";