From 9042843e425180dfc6baf17c341f0907aaaf9746 Mon Sep 17 00:00:00 2001
From: Tesfa Mael <tesfa@wolfssl.com>
Date: Thu, 10 Dec 2020 16:13:30 -0800
Subject: [PATCH] Fix shift and clear digits

---
 wolfcrypt/src/integer.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/wolfcrypt/src/integer.c b/wolfcrypt/src/integer.c
index 95c894353..cd021e7f9 100644
--- a/wolfcrypt/src/integer.c
+++ b/wolfcrypt/src/integer.c
@@ -684,8 +684,10 @@ int mp_mod_2d (mp_int * a, int b, mp_int * c)
     c->dp[x] = 0;
   }
   /* clear the digit that is not completely outside/inside the modulus */
-  c->dp[b / DIGIT_BIT] &= (mp_digit) ((((mp_digit) 1) <<
-              (((mp_digit) b) % DIGIT_BIT)) - ((mp_digit) 1));
+  x = DIGIT_BIT - (b % DIGIT_BIT);
+  if (x != DIGIT_BIT) {
+    c->dp[b / DIGIT_BIT] &= ~((mp_digit)0) >> x;
+  }
   mp_clamp (c);
   return MP_OKAY;
 }