[libc] Add FPBits support for Float128

libc/include/llvm-libc-types/float128.h

@@ -31,6 +31,9 @@ typedef __float128 float128;
 #elif (LDBL_MANT_DIG == 113)
 #define LIBC_TYPES_HAS_FLOAT128
 typedef long double float128;
+#else
+#include "src/__support/FPUtil/float128.h"
+typedef LIBC_NAMESPACE::fputil::Float128 float128;
 #endif
 
 #endif // LLVM_LIBC_TYPES_FLOAT128_H

libc/src/__support/FPUtil/FPBits.h

@@ -26,6 +26,7 @@
 #include "src/__support/math_extras.h"             // mask_trailing_ones
 #include "src/__support/sign.h"                    // Sign
 #include "src/__support/uint128.h"
+#include "src/__support/FPUtil/float128.h"  //include float128.h
 
 namespace LIBC_NAMESPACE_DECL {
 namespace fputil {
@@ -809,6 +810,8 @@ template <typename T> LIBC_INLINE static constexpr FPType get_fp_type() {
   else if constexpr (cpp::is_same_v<UnqualT, float128>)
     return FPType::IEEE754_Binary128;
 #endif
+  else if constexpr (cpp::is_same_v<UnqualT, LIBC_NAMESPACE::fputil::Float128>)
+    return FPType::IEEE754_Binary128;
   else if constexpr (cpp::is_same_v<UnqualT, bfloat16>)
     return FPType::BFloat16;
   else
@@ -825,7 +828,8 @@ template <typename T> LIBC_INLINE static constexpr FPType get_fp_type() {
 // It derives its functionality to FPRepImpl above.
 template <typename T>
 struct FPBits final : public internal::FPRepImpl<get_fp_type<T>(), FPBits<T>> {
-  static_assert(cpp::is_floating_point_v<T>,
+  static_assert(cpp::is_floating_point_v<T>
+                ||cpp::is_same_v<T, LIBC_NAMESPACE::fputil::Float128>,
                 "FPBits instantiated with invalid type.");
   using UP = internal::FPRepImpl<get_fp_type<T>(), FPBits<T>>;
   using StorageType = typename UP::StorageType;

libc/src/__support/FPUtil/float128.h

@@ -0,0 +1,37 @@
+//===-- Float128 software wrapper ----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines a minimal software-backed Float128 wrapper type used when
+// the host compiler does not provide a native 128-bit floating-point type.
+// The wrapper currently only stores the raw 128-bit representation.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SUPPORT_FPUTIL_FLOAT128_H
+#define LLVM_LIBC_SRC_SUPPORT_FPUTIL_FLOAT128_H
+
+#include "src/__support/uint128.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace fputil {
+
+class Float128 {
+private:
+  UInt128 bits_ = 0;
+
+public:
+    constexpr Float128() = default;
+
+    constexpr explicit Float128(UInt128 value) : bits_(value) {}
+
+    constexpr UInt128 get_bits() const { return bits_; }
+};
+} // namespace fputil
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_FLOAT128_H

libc/test/src/__support/FPUtil/fpbits_test.cpp

@@ -778,3 +778,9 @@ TEST(LlvmLibcFPBitsTest, Float128Type) {
   EXPECT_EQ(quiet_nan.is_quiet_nan(), true);
 }
 #endif // LIBC_TYPES_HAS_FLOAT128
+
+TEST(LlvmLibcFPBitsTest, Float128WrapperInstantiation) {
+  LIBC_NAMESPACE::fputil::Float128 x;
+  LIBC_NAMESPACE::fputil::FPBits<LIBC_NAMESPACE::fputil::Float128> bits(x);
+  EXPECT_TRUE(bits.is_zero());
+}