LibJS: Add modulo(x, y) overload for Crypto::{Unsigned,Signed}BigInteger

Just like with integral and floating numbers, doing it manually is
error-prone: when we get a negative remainder, y has to be added to the
result to match the spec's modulo.
Solve this by just adding another (templated) overload to also permit
using the function for LibCrypto BigInts.

1 files changed, 10 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/AbstractOperations.h b/Userland/Libraries/LibJS/Runtime/AbstractOperations.h
index e9e6a7595d..de155d7e78 100644
--- a/Userland/Libraries/LibJS/Runtime/AbstractOperations.h
+++ b/Userland/Libraries/LibJS/Runtime/AbstractOperations.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Forward.h>
+#include <LibCrypto/Forward.h>
 #include <LibJS/AST.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Runtime/GlobalObject.h>
@@ -91,4 +92,13 @@ auto modulo(T x, U y) requires(IsArithmetic<T>, IsArithmetic<U>)
     }
 }
 
+auto modulo(Crypto::BigInteger auto const& x, Crypto::BigInteger auto const& y)
+{
+    VERIFY(y != "0"_bigint);
+    auto result = x.divided_by(y).remainder;
+    if (result.is_negative())
+        result = result.plus(y);
+    return result;
+}
+
 }