Improve montgomeryAdd implementation (matter-labs#113)

* Make montgomery add more efficient * Fix add montgomery for edge case * Add montgomery add improvement for ecPairing
lambdaclass · Sep 21, 2023 · f660dca · f660dca
1 parent e155896
commit f660dca
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Showing 3 changed files with 12 additions and 3 deletions.
diff --git a/precompiles/EcAdd.yul b/precompiles/EcAdd.yul
@@ -201,7 +201,10 @@ object "EcAdd" {
             }
 
             function montgomeryAdd(augend, addend) -> ret {
-                ret := addmod(augend, addend, P())
+                ret := add(augend, addend)
+                if iszero(lt(ret, P())) {
+                    ret := sub(ret, P())
+                }
             }
 
             function montgomerySub(minuend, subtrahend) -> ret {

diff --git a/precompiles/EcMul.yul b/precompiles/EcMul.yul
@@ -179,7 +179,10 @@ object "EcMul" {
             }
 
             function montgomeryAdd(augend, addend) -> ret {
-                ret := addmod(augend, addend, P())
+                ret := add(augend, addend)
+                if iszero(lt(ret, P())) {
+                    ret := sub(ret, P())
+                }
             }
 
             function montgomerySub(minuend, subtrahend) -> ret {

diff --git a/precompiles/EcPairing.yul b/precompiles/EcPairing.yul
@@ -257,7 +257,10 @@ object "EcPairing" {
             /// @param addend The addend in Montgomery form.
             /// @return ret The result of the Montgomery addition.
             function montgomeryAdd(augend, addend) -> ret {
-                ret := addmod(augend, addend, P())
+                ret := add(augend, addend)
+                if iszero(lt(ret, P())) {
+                    ret := sub(ret, P())
+                }
             }
 
             /// @notice Computes the Montgomery subtraction.