LibCrypto: Fix bug in big int subtraction

A regression test was added to the suite. This commit also generally simplifies the subtraction method.
Author: https://github.com/itamar8910 Commit: 709c691f38 Pull-request: https://github.com/SerenityOS/serenity/pull/1661 Reviewed-by: https://github.com/Dexesttp Reviewed-by: https://github.com/alimpfard Reviewed-by: https://github.com/awesomekling
2025-09-30 13:19:02 +00:00 · 2020-04-09 16:29:09 +03:00 · 2020-04-09 16:29:09 +03:00 · 709c691f38 · 2024-07-19 07:05:39 +09:00
commit 709c691f38
parent 0d2777752e
2 changed files with 19 additions and 16 deletions
--- a/Userland/test-crypto.cpp
+++ b/Userland/test-crypto.cpp
@ -915,6 +915,15 @@ void bigint_subtraction()
        // this test only verifies that we don't crash on an assertion
        PASS;
    }
+    {
+        I_TEST((BigInteger | Subtraction Regerssion 1));
+        auto num = Crypto::UnsignedBigInteger { 1 }.shift_left(256);
+        if (num.sub(1).words() == Vector<u32> { 4294967295, 4294967295, 4294967295, 4294967295, 4294967295, 4294967295, 4294967295, 4294967295, 0 }) {
+            PASS;
+        } else {
+            FAIL(Incorrect Result);
+        }
+    }
 }

 void bigint_multiplication()