Fix base scalar multiplication (#117)

Author: paberr

CHANGELOG.md

@@ -1,6 +1,7 @@
 # CHANGELOG
 
 ## Pending
+- [\#117](https://github.com/arkworks-rs/r1cs-std/pull/117) Fix result of `precomputed_base_scalar_mul_le` to not discard previous value.
 
 ### Breaking changes
 

src/groups/curves/short_weierstrass/mod.rs

@@ -559,7 +559,7 @@ where
             .map(|(b, c)| (b.borrow().clone(), *c))
             .unzip();
         let base = bases[0];
-        *self = Self::constant(base).scalar_mul_le(bits.iter())?;
+        *self += Self::constant(base).scalar_mul_le(bits.iter())?;
         Ok(())
     }
 }

src/groups/mod.rs

@@ -134,7 +134,7 @@ pub trait CurveVar<C: CurveGroup, ConstraintF: Field>:
             // else, set self = self;
             result = bit.borrow().select(&self_plus_base, &result)?;
         }
-        *self = result;
+        *self += result;
         Ok(())
     }