From b7b8126ccfcb9dbcefa4f97f1496c0b69f862469 Mon Sep 17 00:00:00 2001
From: therealyingtong <yingtong@z.cash>
Date: Sun, 13 Jun 2021 23:19:12 +0800
Subject: [PATCH] spec.rs: Add lebs2ip function bounded on const generic L.

Co-authored-by: Jack Grigg <jack@electriccoin.co>
---
 src/primitives/sinsemilla.rs |  2 +-
 src/spec.rs                  | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/primitives/sinsemilla.rs b/src/primitives/sinsemilla.rs
index 88fd94c6..a95679cf 100644
--- a/src/primitives/sinsemilla.rs
+++ b/src/primitives/sinsemilla.rs
@@ -14,7 +14,7 @@ mod constants;
 mod sinsemilla_s;
 pub use constants::*;
 
-pub fn lebs2ip_k(bits: &[bool]) -> u32 {
+fn lebs2ip_k(bits: &[bool]) -> u32 {
     assert!(bits.len() == K);
     bits.iter()
         .enumerate()
diff --git a/src/spec.rs b/src/spec.rs
index 776197cc..ccd1cf78 100644
--- a/src/spec.rs
+++ b/src/spec.rs
@@ -179,6 +179,18 @@ pub(crate) fn extract_p_bottom(point: CtOption<pallas::Point>) -> CtOption<palla
     point.map(|p| extract_p(&p))
 }
 
+/// The u64 integer represented by an L-bit little-endian bitstring.
+///
+/// Panics
+///
+/// Panics if the bitstring is longer than 64 bits.
+pub fn lebs2ip<const L: usize>(bits: &[bool; L]) -> u64 {
+    assert!(L <= 64);
+    bits.iter()
+        .enumerate()
+        .fold(0u64, |acc, (i, b)| acc + if *b { 1 << i } else { 0 })
+}
+
 #[cfg(test)]
 mod tests {
     use group::Group;