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      1 /*
      2  * Copyright (C) 2011 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ANDROID_TRAITS_H
     18 #define ANDROID_TRAITS_H
     19 
     20 // -----------------------------------------------------------------------
     21 // Typelists
     22 
     23 namespace android {
     24 
     25 // end-of-list marker
     26 class NullType {};
     27 
     28 // type-list node
     29 template <typename T, typename U>
     30 struct TypeList {
     31     typedef T Head;
     32     typedef U Tail;
     33 };
     34 
     35 // helpers to build typelists
     36 #define TYPELIST_1(T1) TypeList<T1, NullType>
     37 #define TYPELIST_2(T1, T2) TypeList<T1, TYPELIST_1(T2)>
     38 #define TYPELIST_3(T1, T2, T3) TypeList<T1, TYPELIST_2(T2, T3)>
     39 #define TYPELIST_4(T1, T2, T3, T4) TypeList<T1, TYPELIST_3(T2, T3, T4)>
     40 
     41 // typelists algorithms
     42 namespace TL {
     43 template <typename TList, typename T> struct IndexOf;
     44 
     45 template <typename T>
     46 struct IndexOf<NullType, T> {
     47     enum { value = -1 };
     48 };
     49 
     50 template <typename T, typename Tail>
     51 struct IndexOf<TypeList<T, Tail>, T> {
     52     enum { value = 0 };
     53 };
     54 
     55 template <typename Head, typename Tail, typename T>
     56 struct IndexOf<TypeList<Head, Tail>, T> {
     57 private:
     58     enum { temp = IndexOf<Tail, T>::value };
     59 public:
     60     enum { value = temp == -1 ? -1 : 1 + temp };
     61 };
     62 
     63 }; // namespace TL
     64 
     65 // type selection based on a boolean
     66 template <bool flag, typename T, typename U>
     67 struct Select {
     68     typedef T Result;
     69 };
     70 template <typename T, typename U>
     71 struct Select<false, T, U> {
     72     typedef U Result;
     73 };
     74 
     75 // -----------------------------------------------------------------------
     76 // Type traits
     77 
     78 template <typename T>
     79 class TypeTraits {
     80     typedef TYPELIST_4(
     81             unsigned char, unsigned short,
     82             unsigned int, unsigned long int) UnsignedInts;
     83 
     84     typedef TYPELIST_4(
     85             signed char, signed short,
     86             signed int, signed long int) SignedInts;
     87 
     88     typedef TYPELIST_1(
     89             bool) OtherInts;
     90 
     91     typedef TYPELIST_3(
     92             float, double, long double) Floats;
     93 
     94     template<typename U> struct PointerTraits {
     95         enum { result = false };
     96         typedef NullType PointeeType;
     97     };
     98     template<typename U> struct PointerTraits<U*> {
     99         enum { result = true };
    100         typedef U PointeeType;
    101     };
    102 
    103 public:
    104     enum { isStdUnsignedInt = TL::IndexOf<UnsignedInts, T>::value >= 0 };
    105     enum { isStdSignedInt   = TL::IndexOf<SignedInts,   T>::value >= 0 };
    106     enum { isStdIntegral    = TL::IndexOf<OtherInts,    T>::value >= 0 || isStdUnsignedInt || isStdSignedInt };
    107     enum { isStdFloat       = TL::IndexOf<Floats,       T>::value >= 0 };
    108     enum { isPointer        = PointerTraits<T>::result };
    109     enum { isStdArith       = isStdIntegral || isStdFloat };
    110 
    111     // best parameter type for given type
    112     typedef typename Select<isStdArith || isPointer, T, const T&>::Result ParameterType;
    113 };
    114 
    115 // -----------------------------------------------------------------------
    116 }; // namespace android
    117 
    118 #endif /* ANDROID_TRAITS_H */
    119