[英]C++ template specialization for specific values
I have struct Opers
with some arithmetic operations: mult()
, div()
, mod()
. 我有一些带有算术运算的struct Opers
: mult()
, div()
, mod()
。
And I need to specialize template for certain values of n
. 我需要为n
某些值专门化模板。 Here is example for Opers<1>
. 以下是Opers<1>
示例。
But, also I want to do specialization for n
that are powers of 2 ( n = 2,4,8,16, ...) – in this case I can optimize operations mult()
and div()
(using bitwise shift left or right). 但是,我也想为做到专业化n
是2(N = 2,4,8,16,...)的权力-在这种情况下,我可以优化操作mult()
和div()
使用逐左移或者右)。
#include <iostream>
using namespace std;
template<int n> struct Opers {
int mult(int x){
return n*x;
}
int div(int x){
return x / n;
}
int mod(int x){
return x % n;
}
};
template<> struct Opers<1> {
int mult(int x){
return 1;
}
int div(int x){
return x;
}
int mod(int x){
return 0;
}
};
int main() {
Opers<1> el2;
cout << el2.mult(3) <<endl;
}
I'm looking for construction like 我正在寻找像这样的建筑
template<> struct Opers<isPowerOfTwo()>
int mult(int x){
// do smth
}
Is it possible or what manual should I read? 是否有可能或我应该阅读哪些手册?
UPD. UPD。 Using C++11 is allowed, and even would be better. 允许使用C ++ 11,甚至会更好。
In C++11, you could do it this way. 在C ++ 11中,你可以这样做。 First of all, change your primary template so that it accepts a second, dummy parameter: 首先,更改主模板,使其接受第二个虚拟参数:
template<int n, typename = void>
struct Opers
{
// ...
};
Then, write a constexpr
function that determines whether an integer is a power of 2: 然后,编写一个constexpr
函数,用于确定整数是否为2的幂:
constexpr bool is_power_of_two(int x)
{
return (x == 1) || ((x % 2 == 0) && is_power_of_two(x / 2));
}
Finally, use SFINAE to enable or disable the specialization based on the result of your constexpr
function: 最后,使用SFINAE根据constexpr
函数的结果启用或禁用特化:
#include <type_traits>
template<int n>
struct Opers<n, typename std::enable_if<is_power_of_two(n)>::type>
{
// ...
};
template <int N, typename = void>
struct Operations
{
// ....
};
template <int N, typename = std::enable_if<(N & (N - 1))>::type>
struct Operations
{
// ....
};
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