[libc-commits] [libc] [libc] Make `BigInt` bitwise shift consistent with regular integral semantics. (PR #87762)

[Guillaume Chatelet via libc-commits]

================
@@ -122,15 +122,17 @@ template <size_t Bits> struct DyadicFloat {
 
     int exp_lo = exp_hi - static_cast<int>(PRECISION) - 1;
 
-    MantissaType m_hi(mantissa >> shift);
+    MantissaType m_hi =
+        shift >= MantissaType::BITS ? MantissaType(0) : mantissa >> shift;
----------------
gchatelet wrote:

Without these changes the tests are failing, so apparently `shift` may be greater or equal to `BITS`. I also ran the tests with `-fsanitize=undefined` using `__uint128_t` as the `MantissaType` in a separate patch and it reported an out of bound shift at these locations. 

https://github.com/llvm/llvm-project/pull/87762