Zero is only a little bit positive

Author: jack-fortanix

mbedtls/src/bignum/mod.rs

@@ -83,6 +83,7 @@ impl ::core::str::FromStr for Mpi {
 #[derive(Debug,Copy,Clone,Eq,PartialEq)]
 pub enum Sign {
     Negative,
+    Zero,
     Positive,
 }
 
@@ -147,8 +148,11 @@ impl Mpi {
     }
 
     pub fn sign(&self) -> Sign {
-        if self.inner.s < 0 {
+        let cmp = unsafe { mpi_cmp_int(&self.inner, 0) };
+        if cmp < 0 {
             Sign::Negative
+        } else if cmp == 0 {
+            Sign::Zero
         } else {
             Sign::Positive
         }

mbedtls/tests/bignum.rs

@@ -356,7 +356,7 @@ const BASE58_ALPHABET: &[u8] = b"123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmno
 
 fn base58_encode(bits: &[u8]) -> mbedtls::Result<String> {
     let zero = Mpi::new(0)?;
-    assert_eq!(zero.sign(), Sign::Positive);
+    assert_eq!(zero.sign(), Sign::Zero);
     let mut n = Mpi::from_binary(bits)?;
     let radix: i64 = 58;