如何在VexCL向量中找到最大值的索引?我可以找到最大值:
int h[] = {3, 2, 1, 5, 4};
vex::vector<int> d(ctx, 5);
vex::copy(h, d);
vex::Reductor<int, vex::MAX> max(ctx.queue());
int m = max(d);
哪个提供m = 5
,但有没有办法找到最大值的索引ind = 3
?
答案 0 :(得分:2)
你需要
以下是工作代码:
#include <iostream>
#include <vector>
#include <vexcl/vexcl.hpp>
// This function converts two integers to cl_int2
VEX_FUNCTION(cl_int2, make_int2, (int, x)(int, y),
int2 v = {x, y};
return v;
);
// This struct compares OpenCL vector types by the first component.
struct MAX0 {
template <class Tn>
struct impl {
typedef typename vex::cl_scalar_of<Tn>::type T;
// Initial value.
static Tn initial() {
Tn v;
if (std::is_unsigned<T>::value)
v.s[0] = static_cast<T>(0);
else
v.s[0] = -std::numeric_limits<T>::max();
return v;
}
// Device-side function call operator
struct device : vex::UserFunction<device, Tn(Tn, Tn)> {
static std::string name() { return "MAX_" + vex::type_name<Tn>(); }
static std::string body() { return "return prm1.x > prm2.x ? prm1 : prm2;"; }
};
// Host-side function call operator
Tn operator()(Tn a, Tn b) const {
return a.s[0] > b.s[0] ? a : b;
}
};
};
int main(int argc, char *argv[]) {
vex::Context ctx( vex::Filter::Env );
std::vector<int> h = {3, 2, 1, 5, 4};
vex::vector<int> d(ctx, h);
// Create reductor based on MAX0 operation,
// then reduce an expression that encodes both value and position of a
// vector element:
vex::Reductor<cl_int2, MAX0> max(ctx);
cl_int2 m = max(make_int2(d, vex::element_index()));
std::cout << "max value of " << m.s[0] << " at position " << m.s[1] << std::endl;
}
此输出
max value of 5 at position 3