TheRock/rocm-libraries/projects/rocthrust/examples/transform_iterator.cu

// Copyright (c) 2020-2025 Advanced Micro Devices, Inc. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include <thrust/device_vector.h>
#include <thrust/functional.h>
#include <thrust/iterator/counting_iterator.h>
#include <thrust/iterator/transform_iterator.h>
#include <thrust/reduce.h>

#include <iostream>
#include <iterator>
#include <string>

#include "include/host_device.h"

// this functor clamps a value to the range [lo, hi]
template <typename T>
struct clamp
{
  T lo, hi;

  __host__ __device__ clamp(T _lo, T _hi)
      : lo(_lo)
      , hi(_hi)
  {}

  __host__ __device__ T operator()(T x)
  {
    if (x < lo)
    {
      return lo;
    }
    else if (x < hi)
    {
      return x;
    }
    else
    {
      return hi;
    }
  }
};

template <typename T>
struct simple_negate
{
  __host__ __device__ T operator()(T x)
  {
    return -x;
  }
};

template <typename Iterator>
void print_range(const std::string& name, Iterator first, Iterator last)
{
  using T = typename std::iterator_traits<Iterator>::value_type;

  std::cout << name << ": ";
  thrust::copy(first, last, std::ostream_iterator<T>(std::cout, " "));
  std::cout << "\n";
}

int main(void)
{
  // clamp values to the range [1, 5]
  int lo = 1;
  int hi = 5;

  // define some types
  using Vector         = thrust::device_vector<int>;
  using VectorIterator = Vector::iterator;

  // initialize values
  Vector values(8);

  values[0] = 2;
  values[1] = 5;
  values[2] = 7;
  values[3] = 1;
  values[4] = 6;
  values[5] = 0;
  values[6] = 3;
  values[7] = 8;

  print_range("values         ", values.begin(), values.end());

  // define some more types
  using ClampedVectorIterator = thrust::transform_iterator<clamp<int>, VectorIterator>;

  // create a transform_iterator that applies clamp() to the values array
  ClampedVectorIterator cv_begin = thrust::make_transform_iterator(values.begin(), clamp<int>(lo, hi));
  ClampedVectorIterator cv_end   = cv_begin + values.size();

  // now [clamped_begin, clamped_end) defines a sequence of clamped values
  print_range("clamped values ", cv_begin, cv_end);

  ////
  // compute the sum of the clamped sequence with reduce()
  std::cout << "sum of clamped values : " << thrust::reduce(cv_begin, cv_end) << "\n";

  ////
  // combine transform_iterator with other fancy iterators like counting_iterator
  using CountingIterator        = thrust::counting_iterator<int>;
  using ClampedCountingIterator = thrust::transform_iterator<clamp<int>, CountingIterator>;

  CountingIterator count_begin(0);
  CountingIterator count_end(10);

  print_range("sequence         ", count_begin, count_end);

  ClampedCountingIterator cs_begin = thrust::make_transform_iterator(count_begin, clamp<int>(lo, hi));
  ClampedCountingIterator cs_end   = thrust::make_transform_iterator(count_end, clamp<int>(lo, hi));

  print_range("clamped sequence ", cs_begin, cs_end);

  ////
  // combine transform_iterator with another transform_iterator
  using NegatedClampedCountingIterator = thrust::transform_iterator<thrust::negate<int>, ClampedCountingIterator>;

  NegatedClampedCountingIterator ncs_begin = thrust::make_transform_iterator(cs_begin, thrust::negate<int>());
  NegatedClampedCountingIterator ncs_end   = thrust::make_transform_iterator(cs_end, thrust::negate<int>());

  print_range("negated sequence ", ncs_begin, ncs_end);

  ////
  // when a functor does not define result_type, a third template argument must be provided
  using NegatedVectorIterator = thrust::transform_iterator<simple_negate<int>, VectorIterator, int>;

  NegatedVectorIterator nv_begin(values.begin(), simple_negate<int>());
  NegatedVectorIterator nv_end(values.end(), simple_negate<int>());

  print_range("negated values ", nv_begin, nv_end);

  return 0;
}