From 855c8fa7fac20816395003f744b6779e165e37e7 Mon Sep 17 00:00:00 2001
From: Nick Johnson <nick@yonson.dev>
Date: Wed, 28 Jan 2026 12:50:13 -0800
Subject: [PATCH 1/2] Add const hex macro
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Adds a `hex!` macro for parsing hex strings in const contexts. The
implementation is inspired by the hex_lit crate by Martin Habovštiak
(https://github.com/Kixunil/hex_lit).
---
 CHANGELOG.md |  4 ++++
 src/lib.rs   | 67 +++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 68 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5b61392..5d7834c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 0.3.2 - 2025-11-28
+
+- Add `hex!` macro for const hex literal parsing.
+
 # 0.3.1 - 2025-11-24
 
 - Remove `doc_auto_cfg` because it breaks the docs builds on crates.io
diff --git a/src/lib.rs b/src/lib.rs
index a71b9b6..01a8bde 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,7 +4,16 @@
 //!
 //! General purpose hex encoding/decoding library with a conservative MSRV and dependency policy.
 //!
-//! ## Basic Usage
+//! ## Const hex literals
+//!
+//! ```
+//! use hex_conservative::hex;
+//!
+//! const GENESIS: [u8; 32] = hex!("000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f");
+//! ```
+//!
+//! ## Runtime hex parsing
+//!
 //! ```
 //! # #[cfg(feature = "alloc")] {
 //! // In your manifest use the `package` key to improve import ergonomics.
@@ -59,6 +68,38 @@ pub mod parse;
 #[cfg(feature = "serde")]
 pub mod serde;
 
+/// Parses hex strings in const contexts.
+///
+/// Returns `[u8; N]` arrays. The string must have even length.
+#[macro_export]
+macro_rules! hex {
+    ($hex:expr) => {{
+        const _: () = assert!($hex.len() % 2 == 0, "hex string must have even length");
+
+        const fn decode_digit(digit: u8) -> u8 {
+            match digit {
+                b'0'..=b'9' => digit - b'0',
+                b'a'..=b'f' => digit - b'a' + 10,
+                b'A'..=b'F' => digit - b'A' + 10,
+                _ => panic!("invalid hex digit"),
+            }
+        }
+
+        let mut output = [0u8; $hex.len() / 2];
+        let bytes = $hex.as_bytes();
+
+        let mut i = 0;
+        while i < output.len() {
+            let high = decode_digit(bytes[i * 2]);
+            let low = decode_digit(bytes[i * 2 + 1]);
+            output[i] = (high << 4) | low;
+            i += 1;
+        }
+
+        output
+    }};
+}
+
 /// Re-exports of the common crate traits.
 pub mod prelude {
     #[doc(inline)]
@@ -156,13 +197,33 @@ mod table {
 macro_rules! test_hex_unwrap (($hex:expr) => (<Vec<u8> as $crate::FromHex>::from_hex($hex).unwrap()));
 
 #[cfg(test)]
+#[cfg(feature = "alloc")]
 mod tests {
-    use crate::test_hex_unwrap as hex;
+    use alloc::vec::Vec;
 
     #[test]
     fn parse_hex_into_vector() {
-        let got = hex!("deadbeef");
+        let got = crate::test_hex_unwrap!("deadbeef");
         let want = vec![0xde, 0xad, 0xbe, 0xef];
         assert_eq!(got, want)
     }
+
+    #[test]
+    fn hex_macro() {
+        let data = hex!("deadbeef");
+        assert_eq!(data, [0xde, 0xad, 0xbe, 0xef]);
+    }
+
+    #[test]
+    fn hex_macro_case_insensitive() {
+        assert_eq!(hex!("DEADBEEF"), hex!("deadbeef"));
+    }
+
+    #[test]
+    fn hex_macro_const_context() {
+        const HASH: [u8; 32] =
+            hex!("000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f");
+        assert_eq!(HASH[0], 0x00);
+        assert_eq!(HASH[31], 0x6f);
+    }
 }

From 54ec5a43f62da406e7791ccffcff0081584da1f4 Mon Sep 17 00:00:00 2001
From: Nick Johnson <nick@yonson.dev>
Date: Wed, 28 Jan 2026 12:50:21 -0800
Subject: [PATCH 2/2] Bump version to 0.3.2

---
 CHANGELOG.md       | 2 +-
 Cargo-minimal.lock | 2 +-
 Cargo-recent.lock  | 2 +-
 Cargo.toml         | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5d7834c..1f4c4a5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-# 0.3.2 - 2025-11-28
+# 0.3.2 - 2026-01-28
 
 - Add `hex!` macro for const hex literal parsing.
 
diff --git a/Cargo-minimal.lock b/Cargo-minimal.lock
index cde7527..739e85c 100644
--- a/Cargo-minimal.lock
+++ b/Cargo-minimal.lock
@@ -16,7 +16,7 @@ checksum = "5edd69c67b2f8e0911629b7e6b8a34cb3956613cd7c6e6414966dee349c2db4f"
 
 [[package]]
 name = "hex-conservative"
-version = "0.3.1"
+version = "0.3.2"
 dependencies = [
  "arrayvec",
  "serde",
diff --git a/Cargo-recent.lock b/Cargo-recent.lock
index d9e0b99..d236b07 100644
--- a/Cargo-recent.lock
+++ b/Cargo-recent.lock
@@ -10,7 +10,7 @@ checksum = "7c02d123df017efcdfbd739ef81735b36c5ba83ec3c59c80a9d7ecc718f92e50"
 
 [[package]]
 name = "hex-conservative"
-version = "0.3.1"
+version = "0.3.2"
 dependencies = [
  "arrayvec",
  "serde",
diff --git a/Cargo.toml b/Cargo.toml
index ef2dda0..17baad7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "hex-conservative"
-version = "0.3.1"
+version = "0.3.2"
 authors = ["Martin Habovštiak <martin.habovstiak@gmail.com>", "Andrew Poelstra <apoelstra@wpsoftware.net>"]
 license = "CC0-1.0"
 repository = "https://github.com/rust-bitcoin/hex-conservative"