Calculator: Round small number to prevent crash

Small numbers (smaller than 1e-19) can't be displayed in the calculator.
They provoke a division by zero in Keypad::set_value(), as 10^20
overflows.

1 files changed, 16 insertions, 0 deletions

diff --git a/Userland/Applications/Calculator/Calculator.h b/Userland/Applications/Calculator/Calculator.h
index 1ca9fca5c0..91f6c21eff 100644
--- a/Userland/Applications/Calculator/Calculator.h
+++ b/Userland/Applications/Calculator/Calculator.h
@@ -47,6 +47,22 @@ public:
     void clear_error() { m_has_error = false; }
 
 private:
+    static bool should_be_rounded(KeypadValue);
+    static void round(KeypadValue&);
+
+    static constexpr auto rounding_threshold = []() consteval
+    {
+        using used_type = u64;
+
+        auto count = 1;
+        used_type res = 10;
+        while (!__builtin_mul_overflow(res, (used_type)10, &res)) {
+            count++;
+        }
+        return count;
+    }
+    ();
+
     Operation m_operation_in_progress { Operation::None };
     KeypadValue m_saved_argument { (i64)0 };
     KeypadValue m_mem { (i64)0 };