From 47e4bff0ee8e17bddbc96ad4e907439f5ea9feaa Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Wed, 5 Jun 2024 08:39:47 +1000
Subject: [PATCH 1/2] pow: Fix off-by-one error

Length check has an off-by-one error in it, we want the check it include
hex strings of length 32 (eg, 128 bytes).
---
 bitcoin/src/pow.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bitcoin/src/pow.rs b/bitcoin/src/pow.rs
index 1642bef46..01e895a15 100644
--- a/bitcoin/src/pow.rs
+++ b/bitcoin/src/pow.rs
@@ -497,7 +497,7 @@ impl U256 {
 
     // Caller to ensure `s` does not contain a prefix.
     fn from_hex_internal(s: &str) -> Result<Self, ParseIntError> {
-        let (high, low) = if s.len() < 32 {
+        let (high, low) = if s.len() <= 32 {
             let low = parse::hex_u128_unchecked(s)?;
             (0, low)
         } else {

From 3298c0c4b5e9f200f200609b0c1f7051a5eec246 Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Wed, 5 Jun 2024 08:41:02 +1000
Subject: [PATCH 2/2] pow: Unit test from_hex_internal

Add a unit test that fails if put before the "pow: Fix off-by-one error"
patch. Tests that we can correctly parse a 32 character long hex string
into a `U256`.
---
 bitcoin/src/pow.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/bitcoin/src/pow.rs b/bitcoin/src/pow.rs
index 01e895a15..eab1f9e3e 100644
--- a/bitcoin/src/pow.rs
+++ b/bitcoin/src/pow.rs
@@ -1652,6 +1652,14 @@ mod tests {
         assert_eq!(got, val);
     }
 
+    #[test]
+    fn u256_from_hex_32_characters_long() {
+        let hex = "a69b455cd41bb662a69b4555deadbeef";
+        let want = U256(0x00, 0xA69B_455C_D41B_B662_A69B_4555_DEAD_BEEF);
+        let got = U256::from_unprefixed_hex(hex).expect("failed to parse hex");
+        assert_eq!(got, want);
+    }
+
     #[cfg(feature = "serde")]
     #[test]
     fn u256_serde() {