+/// \brief The behavior an operation has on an input of 0.
+enum ZeroBehavior {
+ /// \brief The returned value is undefined.
+ ZB_Undefined,
+ /// \brief The returned value is numeric_limits<T>::max()
+ ZB_Max,
+ /// \brief The returned value is numeric_limits<T>::digits
+ ZB_Width
+};
+
+/// \brief Count number of 0's from the least significant bit to the most
+/// stopping at the first 1.
+///
+/// Only unsigned integral types are allowed.
+///
+/// \param ZB the behavior on an input of 0. Only ZB_Width and ZB_Undefined are
+/// valid arguments.
+template <typename T>
+typename std::enable_if<std::numeric_limits<T>::is_integer &&
+ !std::numeric_limits<T>::is_signed, std::size_t>::type
+countTrailingZeros(T Val, ZeroBehavior ZB = ZB_Width) {
+ (void)ZB;
+
+ if (!Val)
+ return std::numeric_limits<T>::digits;
+ if (Val & 0x1)
+ return 0;
+
+ // Bisection method.
+ std::size_t ZeroBits = 0;
+ T Shift = std::numeric_limits<T>::digits >> 1;
+ T Mask = std::numeric_limits<T>::max() >> Shift;
+ while (Shift) {
+ if ((Val & Mask) == 0) {
+ Val >>= Shift;
+ ZeroBits |= Shift;
+ }
+ Shift >>= 1;
+ Mask >>= Shift;
+ }
+ return ZeroBits;
+}
+
+// Disable signed.
+template <typename T>
+typename std::enable_if<std::numeric_limits<T>::is_integer &&
+ std::numeric_limits<T>::is_signed, std::size_t>::type
+countTrailingZeros(T Val, ZeroBehavior ZB = ZB_Width) LLVM_DELETED_FUNCTION;
+
+#if __GNUC__ >= 4 || _MSC_VER
+template <>
+inline std::size_t countTrailingZeros<uint32_t>(uint32_t Val, ZeroBehavior ZB) {
+ if (ZB != ZB_Undefined && Val == 0)
+ return 32;
+
+#if __has_builtin(__builtin_ctz) || __GNUC_PREREQ(4, 0)
+ return __builtin_ctz(Val);
+#elif _MSC_VER
+ unsigned long Index;
+ _BitScanForward(&Index, Val);
+ return Index;
+#endif
+}
+
+#if !defined(_MSC_VER) || defined(_M_X64)
+template <>
+inline std::size_t countTrailingZeros<uint64_t>(uint64_t Val, ZeroBehavior ZB) {
+ if (ZB != ZB_Undefined && Val == 0)
+ return 64;
+
+#if __has_builtin(__builtin_ctzll) || __GNUC_PREREQ(4, 0)
+ return __builtin_ctzll(Val);
+#elif _MSC_VER
+ unsigned long Index;
+ _BitScanForward64(&Index, Val);
+ return Index;
+#endif
+}
+#endif
+#endif
+
+/// \brief Count number of 0's from the most significant bit to the least
+/// stopping at the first 1.
+///
+/// Only unsigned integral types are allowed.
+///
+/// \param ZB the behavior on an input of 0. Only ZB_Width and ZB_Undefined are
+/// valid arguments.
+template <typename T>
+typename std::enable_if<std::numeric_limits<T>::is_integer &&
+ !std::numeric_limits<T>::is_signed, std::size_t>::type
+countLeadingZeros(T Val, ZeroBehavior ZB = ZB_Width) {
+ (void)ZB;
+
+ if (!Val)
+ return std::numeric_limits<T>::digits;
+
+ // Bisection method.
+ std::size_t ZeroBits = 0;
+ for (T Shift = std::numeric_limits<T>::digits >> 1; Shift; Shift >>= 1) {
+ T Tmp = Val >> Shift;
+ if (Tmp)
+ Val = Tmp;
+ else
+ ZeroBits |= Shift;
+ }
+ return ZeroBits;
+}
+
+// Disable signed.
+template <typename T>
+typename std::enable_if<std::numeric_limits<T>::is_integer &&
+ std::numeric_limits<T>::is_signed, std::size_t>::type
+countLeadingZeros(T Val, ZeroBehavior ZB = ZB_Width) LLVM_DELETED_FUNCTION;
+
+#if __GNUC__ >= 4 || _MSC_VER
+template <>
+inline std::size_t countLeadingZeros<uint32_t>(uint32_t Val, ZeroBehavior ZB) {
+ if (ZB != ZB_Undefined && Val == 0)
+ return 32;
+
+#if __has_builtin(__builtin_clz) || __GNUC_PREREQ(4, 0)
+ return __builtin_clz(Val);
+#elif _MSC_VER
+ unsigned long Index;
+ _BitScanReverse(&Index, Val);
+ return Index ^ 31;
+#endif
+}
+
+#if !defined(_MSC_VER) || defined(_M_X64)
+template <>
+inline std::size_t countLeadingZeros<uint64_t>(uint64_t Val, ZeroBehavior ZB) {
+ if (ZB != ZB_Undefined && Val == 0)
+ return 64;
+
+#if __has_builtin(__builtin_clzll) || __GNUC_PREREQ(4, 0)
+ return __builtin_clzll(Val);
+#elif _MSC_VER
+ unsigned long Index;
+ _BitScanReverse64(&Index, Val);
+ return Index ^ 63;
+#endif
+}
+#endif
+#endif