[llvm] [libc] [libc] Make BigInt bit_cast-able to compatible types (PR #74837)

[Guillaume Chatelet via llvm-commits]

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@@ -6,23 +6,73 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "src/__support/CPP/bit.h" // bit_cast
 #include "src/__support/CPP/optional.h"
+#include "src/__support/CPP/type_traits.h" // is_trivially_constructible
 #include "src/__support/UInt.h"
+#include "src/__support/macros/properties/float.h" // LIBC_COMPILER_HAS_FLOAT128
 
 #include "test/UnitTest/Test.h"
 
-// We want to test LIBC_NAMESPACE::cpp::UInt<128> explicitly. So, for
+#include <math.h> // HUGE_VALF, HUGE_VALF
+
+namespace LIBC_NAMESPACE {
+
+using LL_UInt64 = cpp::UInt<64>;
+// We want to test cpp::UInt<128> explicitly. So, for
 // convenience, we use a sugar which does not conflict with the UInt128 type
 // which can resolve to __uint128_t if the platform has it.
-using LL_UInt128 = LIBC_NAMESPACE::cpp::UInt<128>;
-using LL_UInt192 = LIBC_NAMESPACE::cpp::UInt<192>;
-using LL_UInt256 = LIBC_NAMESPACE::cpp::UInt<256>;
-using LL_UInt320 = LIBC_NAMESPACE::cpp::UInt<320>;
-using LL_UInt512 = LIBC_NAMESPACE::cpp::UInt<512>;
-using LL_UInt1024 = LIBC_NAMESPACE::cpp::UInt<1024>;
+using LL_UInt128 = cpp::UInt<128>;
+using LL_UInt192 = cpp::UInt<192>;
+using LL_UInt256 = cpp::UInt<256>;
+using LL_UInt320 = cpp::UInt<320>;
+using LL_UInt512 = cpp::UInt<512>;
+using LL_UInt1024 = cpp::UInt<1024>;
+
+using LL_Int128 = cpp::Int<128>;
+using LL_Int192 = cpp::Int<192>;
+
+TEST(LlvmLibcUIntClassTest, BitCastToFromDouble) {
+  static_assert(cpp::is_trivially_constructible<LL_UInt64>::value);
+  static_assert(cpp::is_trivially_copyable<LL_UInt64>::value);
+  static_assert(sizeof(LL_UInt64) == sizeof(double));
+  const double inf = HUGE_VAL;
+  const double max = DBL_MAX;
+  const double array[] = {0.0f, 0.1f, 1.0f, max, inf};
----------------
gchatelet wrote:

Thx for noticing. I started with `float`s but moved to `double`s (`BigInt` cannot be 32-bit wide).

https://github.com/llvm/llvm-project/pull/74837