[libc-commits] [libc] ba4d369 - [libc] Make BigInt bit_cast-able to compatible types (#75063)
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Thu Dec 21 01:51:27 PST 2023
Author: Guillaume Chatelet
Date: 2023-12-21T10:51:23+01:00
New Revision: ba4d36951f1deaf24dce526900a2d6dbdefa377b
URL: https://github.com/llvm/llvm-project/commit/ba4d36951f1deaf24dce526900a2d6dbdefa377b
DIFF: https://github.com/llvm/llvm-project/commit/ba4d36951f1deaf24dce526900a2d6dbdefa377b.diff
LOG: [libc] Make BigInt bit_cast-able to compatible types (#75063)
This is a second take on #74837 to fix #74258
Added:
Modified:
libc/src/__support/CPP/bit.h
libc/src/__support/FPUtil/FPBits.h
libc/src/__support/UInt.h
libc/test/src/__support/uint_test.cpp
Removed:
################################################################################
diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 4de142b56165b6..122f6b8c332810 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -29,10 +29,10 @@ namespace LIBC_NAMESPACE::cpp {
// UB in the implementation.
template <
typename To, typename From,
- typename = cpp::enable_if_t<sizeof(To) == sizeof(From)>,
- typename = cpp::enable_if_t<cpp::is_trivially_constructible<To>::value>,
- typename = cpp::enable_if_t<cpp::is_trivially_copyable<To>::value>,
- typename = cpp::enable_if_t<cpp::is_trivially_copyable<From>::value>>
+ typename = cpp::enable_if_t<sizeof(To) == sizeof(From) &&
+ cpp::is_trivially_constructible<To>::value &&
+ cpp::is_trivially_copyable<To>::value &&
+ cpp::is_trivially_copyable<From>::value>>
LIBC_INLINE constexpr To bit_cast(const From &from) {
MSAN_UNPOISON(&from, sizeof(From));
#if LIBC_HAS_BUILTIN(__builtin_bit_cast)
diff --git a/libc/src/__support/FPUtil/FPBits.h b/libc/src/__support/FPUtil/FPBits.h
index 37e2820eab8553..b13ce80f94f6e6 100644
--- a/libc/src/__support/FPUtil/FPBits.h
+++ b/libc/src/__support/FPUtil/FPBits.h
@@ -11,6 +11,7 @@
#include "src/__support/CPP/bit.h"
#include "src/__support/CPP/type_traits.h"
+#include "src/__support/UInt128.h"
#include "src/__support/common.h"
#include "src/__support/macros/attributes.h" // LIBC_INLINE
diff --git a/libc/src/__support/UInt.h b/libc/src/__support/UInt.h
index cfd495c5861851..79e05940f02773 100644
--- a/libc/src/__support/UInt.h
+++ b/libc/src/__support/UInt.h
@@ -30,7 +30,7 @@ template <size_t Bits, bool Signed> struct BigInt {
static_assert(Bits > 0 && Bits % 64 == 0,
"Number of bits in BigInt should be a multiple of 64.");
LIBC_INLINE_VAR static constexpr size_t WORDCOUNT = Bits / 64;
- uint64_t val[WORDCOUNT]{};
+ cpp::array<uint64_t, WORDCOUNT> val{};
LIBC_INLINE_VAR static constexpr uint64_t MASK32 = 0xFFFFFFFFu;
@@ -954,6 +954,48 @@ struct make_signed<UInt<Bits>> : type_identity<Int<Bits>> {
"Number of bits in Int should be a multiple of 64.");
};
+namespace internal {
+template <typename T> struct is_custom_uint : cpp::false_type {};
+template <size_t Bits> struct is_custom_uint<UInt<Bits>> : cpp::true_type {};
+} // namespace internal
+
+// bit_cast to UInt
+// Note: The standard scheme for SFINAE selection is to have exactly one
+// function instanciation valid at a time. This is usually done by having a
+// predicate in one function and the negated predicate in the other one.
+// e.g.
+// template<typename = cpp::enable_if_t< is_custom_uint<To>::value == true> ...
+// template<typename = cpp::enable_if_t< is_custom_uint<To>::value == false> ...
+//
+// Unfortunately this would make the default 'cpp::bit_cast' aware of
+// 'is_custom_uint' (or any other customization). To prevent exposing all
+// customizations in the original function, we create a
diff erent function with
+// four 'typename's instead of three - otherwise it would be considered as a
+// redeclaration of the same function leading to "error: template parameter
+// redefines default argument".
+template <typename To, typename From,
+ typename = cpp::enable_if_t<sizeof(To) == sizeof(From) &&
+ cpp::is_trivially_copyable<To>::value &&
+ cpp::is_trivially_copyable<From>::value>,
+ typename = cpp::enable_if_t<internal::is_custom_uint<To>::value>>
+LIBC_INLINE constexpr To bit_cast(const From &from) {
+ To out;
+ using Storage = decltype(out.val);
+ out.val = cpp::bit_cast<Storage>(from);
+ return out;
+}
+
+// bit_cast from UInt
+template <
+ typename To, size_t Bits,
+ typename = cpp::enable_if_t<sizeof(To) == sizeof(UInt<Bits>) &&
+ cpp::is_trivially_constructible<To>::value &&
+ cpp::is_trivially_copyable<To>::value &&
+ cpp::is_trivially_copyable<UInt<Bits>>::value>>
+LIBC_INLINE constexpr To bit_cast(const UInt<Bits> &from) {
+ return cpp::bit_cast<To>(from.val);
+}
+
} // namespace LIBC_NAMESPACE::cpp
#endif // LLVM_LIBC_SRC___SUPPORT_UINT_H
diff --git a/libc/test/src/__support/uint_test.cpp b/libc/test/src/__support/uint_test.cpp
index 971bac55bd9d3f..0ad72c35645c4b 100644
--- a/libc/test/src/__support/uint_test.cpp
+++ b/libc/test/src/__support/uint_test.cpp
@@ -10,19 +10,62 @@
#include "src/__support/UInt.h"
#include "test/UnitTest/Test.h"
+#include <math.h> // HUGE_VALF, HUGE_VALF
-// We want to test LIBC_NAMESPACE::cpp::UInt<128> explicitly. So, for
+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_copyable<LL_UInt64>::value);
+ static_assert(sizeof(LL_UInt64) == sizeof(double));
+ const double inf = HUGE_VAL;
+ const double max = DBL_MAX;
+ const double array[] = {0.0, 0.1, 1.0, max, inf};
+ for (double value : array) {
+ LL_UInt64 back = cpp::bit_cast<LL_UInt64>(value);
+ double forth = cpp::bit_cast<double>(back);
+ EXPECT_TRUE(value == forth);
+ }
+}
-using LL_Int128 = LIBC_NAMESPACE::cpp::Int<128>;
-using LL_Int192 = LIBC_NAMESPACE::cpp::Int<192>;
+#ifdef __SIZEOF_INT128__
+TEST(LlvmLibcUIntClassTest, BitCastToFromNativeUint128) {
+ static_assert(cpp::is_trivially_copyable<LL_UInt128>::value);
+ static_assert(sizeof(LL_UInt128) == sizeof(__uint128_t));
+ const __uint128_t array[] = {0, 1, ~__uint128_t(0)};
+ for (__uint128_t value : array) {
+ LL_UInt128 back = cpp::bit_cast<LL_UInt128>(value);
+ __uint128_t forth = cpp::bit_cast<__uint128_t>(back);
+ EXPECT_TRUE(value == forth);
+ }
+}
+#endif
+
+#ifdef LIBC_COMPILER_HAS_FLOAT128
+TEST(LlvmLibcUIntClassTest, BitCastToFromNativeFloat128) {
+ static_assert(cpp::is_trivially_copyable<LL_UInt128>::value);
+ static_assert(sizeof(LL_UInt128) == sizeof(float128));
+ const float128 array[] = {0, 0.1, 1};
+ for (float128 value : array) {
+ LL_UInt128 back = cpp::bit_cast<LL_UInt128>(value);
+ float128 forth = cpp::bit_cast<float128>(back);
+ EXPECT_TRUE(value == forth);
+ }
+}
+#endif
TEST(LlvmLibcUIntClassTest, BasicInit) {
LL_UInt128 half_val(12345);
@@ -634,3 +677,5 @@ TEST(LlvmLibcUIntClassTest, ConstructorFromUInt128Tests) {
}
#endif // __SIZEOF_INT128__
+
+} // namespace LIBC_NAMESPACE
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