From 42eadef82ffbdea337f033135aa022b2070eb160 Mon Sep 17 00:00:00 2001
From: therealyingtong <yingtong@z.cash>
Date: Sun, 6 Jun 2021 12:11:15 +0800
Subject: [PATCH] sinsemilla::message.rs: Add MessageSubPiece.to_field_elem()
 method

---
 src/circuit/gadget/sinsemilla/message.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/circuit/gadget/sinsemilla/message.rs b/src/circuit/gadget/sinsemilla/message.rs
index f5b1a2990..b7af5e826 100644
--- a/src/circuit/gadget/sinsemilla/message.rs
+++ b/src/circuit/gadget/sinsemilla/message.rs
@@ -128,3 +128,17 @@ impl<F: FieldExt, const K: usize> From<(Option<F>, std::ops::Range<usize>)>
         }
     }
 }
+
+impl<F: FieldExt, const K: usize> MessageSubPiece<F, K> {
+    pub fn to_field_elem(self) -> Option<F> {
+        self.field_elem.map(|value| {
+            let bits = &value
+                .to_le_bits()
+                .iter()
+                .by_val()
+                .take(F::NUM_BITS as usize)
+                .collect::<Vec<_>>()[self.bit_range];
+            bits_to_field_elem(bits)
+        })
+    }
+}