diff --git a/libc/utils/FPUtil/FloatProperties.h b/libc/utils/FPUtil/FloatProperties.h
--- a/libc/utils/FPUtil/FloatProperties.h
+++ b/libc/utils/FPUtil/FloatProperties.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_LIBC_UTILS_FPUTIL_FLOAT_PROPERTIES_H
 #define LLVM_LIBC_UTILS_FPUTIL_FLOAT_PROPERTIES_H
 
+#include "PlatformDefs.h"
 #include <stdint.h>
 
 namespace __llvm_libc {
@@ -24,6 +25,7 @@
   static constexpr uint32_t bitWidth = sizeof(BitsType) << 3;
 
   static constexpr uint32_t mantissaWidth = 23;
+  static constexpr uint32_t exponentWidth = 8;
   static constexpr BitsType mantissaMask = 0x007fffffU;
   static constexpr BitsType signMask = 0x80000000U;
   static constexpr BitsType exponentMask = ~(signMask | mantissaMask);
@@ -43,6 +45,7 @@
   static constexpr uint32_t bitWidth = sizeof(BitsType) << 3;
 
   static constexpr uint32_t mantissaWidth = 52;
+  static constexpr uint32_t exponentWidth = 11;
   static constexpr BitsType mantissaMask = 0x000fffffffffffffU;
   static constexpr BitsType signMask = 0x8000000000000000ULL;
   static constexpr BitsType exponentMask = ~(signMask | mantissaMask);
@@ -54,6 +57,83 @@
   static constexpr BitsType quietNaNMask = 0x0008000000000000ULL;
 };
 
+// Properties for long double on Windows platform, same as double precision.
+#if defined(LONG_DOUBLE_IS_DOUBLE)
+template <> struct FloatProperties<long double> {
+  typedef uint64_t BitsType;
+  static_assert(sizeof(BitsType) == sizeof(double),
+                "Unexpected size of 'double' type.");
+
+  static constexpr uint32_t bitWidth = FloatProperties<double>::bitWidth;
+
+  static constexpr uint32_t mantissaWidth =
+      FloatProperties<double>::mantissaWidth;
+  static constexpr uint32_t exponentWidth =
+      FloatProperties<double>::exponentWidth;
+  static constexpr BitsType mantissaMask =
+      FloatProperties<double>::mantissaMask;
+  static constexpr BitsType signMask = FloatProperties<double>::signMask;
+  static constexpr BitsType exponentMask =
+      FloatProperties<double>::exponentMask;
+  static constexpr uint32_t exponentOffset =
+      FloatProperties<double>::exponentOffset;
+
+  // If a number x is a NAN, then it is a quiet NAN if:
+  //   QuietNaNMask & bits(x) != 0
+  // Else, it is a signalling NAN.
+  static constexpr BitsType quietNaNMask =
+      FloatProperties<double>::quietNaNMask;
+};
+#endif
+
+// Properties for long double on non-Windows x86 platforms.
+#if defined(SPECIAL_X86_LONG_DOUBLE)
+template <> struct FloatProperties<long double> {
+  typedef __uint128_t BitsType;
+  static_assert(sizeof(BitsType) == sizeof(long double),
+                "Unexpected size of 'long double' type.");
+
+  static constexpr uint32_t bitWidth = sizeof(BitsType) << 3;
+
+  static constexpr uint32_t mantissaWidth = 64;
+  static constexpr uint32_t exponentWidth = 15;
+  static constexpr BitsType mantissaMask = 0xffffffffffffffffU;
+  static constexpr BitsType signMask = (BitsType)0x00008000U << 64;
+  static constexpr BitsType exponentMask = ~(signMask | mantissaMask);
+  static constexpr uint32_t exponentOffset = 16383;
+  // If a number x is a NAN, then it is a quiet NAN if:
+  //   QuietNaNMask & bits(x) != 0
+  // Else, it is a signalling NAN.
+  static constexpr BitsType quietNaNMask = 0x8000000000000000U;
+};
+#endif
+
+// Properties for long double on non x86 platform.
+#if !defined(SPECIAL_X86_LONG_DOUBLE)
+template <> struct FloatProperties<long double> {
+  typedef __uint128_t BitsType;
+  static_assert(sizeof(BitsType) == sizeof(long double),
+                "Unexpected size of 'long double' type.");
+
+  static constexpr uint32_t bitWidth = sizeof(BitsType) << 3;
+
+  static constexpr uint32_t mantissaWidth = 112;
+  static constexpr uint32_t exponentWidth = 15;
+  static constexpr BitsType mantissaMask =
+      ((BitsType)0x0000ffffffffffffU << 64) | (BitsType)0xffffffffffffffffU;
+  static constexpr BitsType signMask = (BitsType)0x8000000000000000U << 64;
+  static constexpr BitsType exponentMask = ~(signMask | mantissaMask);
+  static constexpr uint32_t exponentOffset = 16383;
+
+  // If a number x is a NAN, then it is a quiet NAN if:
+  //   QuietNaNMask & bits(x) != 0
+  // Else, it is a signalling NAN.
+  static constexpr BitsType quietNaNMask =
+      (BitsType)0x0000800000000000U
+      << 64; // Has the most significant bit in the mantissa set to one.
+};
+#endif
+
 // Define the float type corresponding to the BitsType.
 template <typename BitsType> struct FloatType;
 
@@ -69,6 +149,12 @@
   typedef double Type;
 };
 
+template <> struct FloatType<__uint128_t> {
+  static_assert(sizeof(__uint128_t) == sizeof(long double),
+                "Unexpected size of 'double' type.");
+  typedef long double Type;
+};
+
 template <typename BitsType>
 using FloatTypeT = typename FloatType<BitsType>::Type;