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#include <thrust/device_vector.h>
#include <thrust/functional.h>
#include <thrust/transform.h>
#include <iostream>
// This example demonstrates the use of placeholders to implement
// the SAXPY operation (i.e. Y[i] = a * X[i] + Y[i]).
//
// Placeholders enable developers to write concise inline expressions
// instead of full functors for many simple operations. For example,
// the placeholder expression "_1 + _2" means to add the first argument,
// represented by _1, to the second argument, represented by _2.
// The names _1, _2, _3, _4 ... _10 represent the first ten arguments
// to the function.
//
// In this example, the placeholder expression "a * _1 + _2" is used
// to implement the SAXPY operation. Note that the placeholder
// implementation is considerably shorter and written inline.
// allows us to use "_1" instead of "thrust::placeholders::_1"
using namespace thrust::placeholders;
// implementing SAXPY with a functor is cumbersome and verbose
struct saxpy_functor
: public thrust::binary_function<float, float, float>
{
float a;
saxpy_functor(float a) : a(a) {}
__host__ __device__
float operator()(float x, float y)
{
return a * x + y;
}
};
int main(void)
{
// input data
float a = 2.0f;
float x[4] = {1, 2, 3, 4};
float y[4] = {1, 1, 1, 1};
// SAXPY implemented with a functor (function object)
{
thrust::device_vector<float> X(x, x + 4);
thrust::device_vector<float> Y(y, y + 4);
thrust::transform(X.begin(), X.end(), // input range #1
Y.begin(), // input range #2
Y.begin(), // output range
saxpy_functor(a)); // functor
std::cout << "SAXPY (functor method)" << std::endl;
for (size_t i = 0; i < 4; i++)
std::cout << a << " * " << x[i] << " + " << y[i] << " = " << Y[i] << std::endl;
}
// SAXPY implemented with a placeholders
{
thrust::device_vector<float> X(x, x + 4);
thrust::device_vector<float> Y(y, y + 4);
thrust::transform(X.begin(), X.end(), // input range #1
Y.begin(), // input range #2
Y.begin(), // output range
a * _1 + _2); // placeholder expression
std::cout << "SAXPY (placeholder method)" << std::endl;
for (size_t i = 0; i < 4; i++)
std::cout << a << " * " << x[i] << " + " << y[i] << " = " << Y[i] << std::endl;
}
return 0;
}
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