Add comment for clearing flags, remove dead code

Author: jayz22

soroban-sdk/src/crypto/bls12_381.rs

@@ -206,10 +206,7 @@ impl Neg for Fp {
             1873798617647539866,
         ]);
         // Compute modulus - value
-        let borrow = res.sub_with_borrow(&fp_bigint);
-        if borrow {
-            sdk_panic!("invalid input - Fp is larger than the field modulus")
-        }
+        res.sub_with_borrow(&fp_bigint);
         let mut bytes = [0u8; 48];
         res.copy_into_array(&mut bytes);
         Fp::from_array(&self.env(), &bytes)
@@ -230,14 +227,6 @@ impl G1Affine {
     }
 }
 
-// impl TryFromVal<Env, Val> for G1Affine {
-//     type Error = ConversionError;
-
-//     fn try_from_val(env: &Env, v: &Val) -> Result<Self, Self::Error> {
-//         Ok(G1Affine(BytesN::try_from_val(env, v)?))
-//     }
-// }
-
 impl Add for G1Affine {
     type Output = G1Affine;
 

soroban-sdk/src/testutils/arbitrary.rs

@@ -697,7 +697,13 @@ mod objects {
 
         fn try_from_val(env: &Env, v: &ArbitraryG1Affine) -> Result<Self, Self::Error> {
             let mut bytes = v.bytes;
-            bytes[0] &= 0b0001_1111; // Clear the top 3 bits
+            // the top 3 bits in a G1 point are reserved for flags:
+            // compression_flag (bit 0), infinity_flag (bit 1) and sort_flag
+            // (bit 2). Only infinity_flag is possible to be set, in which case
+            // the rest of the bytes must be zeros. The host will reject any
+            // invalid input. Clearing the flags here just to give it better
+            // chance of a valid input.
+            bytes[0] &= 0b0001_1111;
             Ok(G1Affine::from_array(env, &bytes))
         }
     }
@@ -717,7 +723,13 @@ mod objects {
 
         fn try_from_val(env: &Env, v: &ArbitraryG2Affine) -> Result<Self, Self::Error> {
             let mut bytes = v.bytes;
-            bytes[0] &= 0b0001_1111; // Clear the top 3 bits
+            // the top 3 bits in a G1 point are reserved for flags:
+            // compression_flag (bit 0), infinity_flag (bit 1) and sort_flag
+            // (bit 2). Only infinity_flag is possible to be set, in which case
+            // the rest of the bytes must be zeros. The host will reject any
+            // invalid input. Clearing the flags here just to give it better
+            // chance of a valid input.
+            bytes[0] &= 0b0001_1111;
             Ok(G2Affine::from_array(env, &bytes))
         }
     }