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#include <thrust/device_vector.h>
#include <thrust/reduce.h>
#include <thrust/functional.h>
#include <thrust/inner_product.h>
#include <iostream>
// This example computes the number of words in a text sample
// with a single call to thrust::inner_product. The algorithm
// counts the number of characters which start a new word, i.e.
// the number of characters where input[i] is an alphabetical
// character and input[i-1] is not an alphabetical character.
// determines whether the character is alphabetical
__host__ __device__
bool is_alpha(const char c)
return (c >= 'A' && c <= 'z');
// determines whether the right character begins a new word
struct is_word_start
: public thrust::binary_function<const char&, const char&, bool>
__host__ __device__
bool operator()(const char& left, const char& right) const
return is_alpha(right) && !is_alpha(left);
int word_count(const thrust::device_vector<char>& input)
// check for empty string
if (input.empty())
return 0;
// compute the number characters that start a new word
int wc = thrust::inner_product(input.begin(), input.end() - 1, // sequence of left characters
input.begin() + 1, // sequence of right characters
0, // initialize sum to 0
thrust::plus<int>(), // sum values together
is_word_start()); // how to compare the left and right characters
// if the first character is alphabetical, then it also begins a word
if (is_alpha(input.front()))
return wc;
int main(void)
// Paragraph from 'The Raven' by Edgar Allan Poe
const char raw_input[] = " But the raven, sitting lonely on the placid bust, spoke only,\n"
" That one word, as if his soul in that one word he did outpour.\n"
" Nothing further then he uttered - not a feather then he fluttered -\n"
" Till I scarcely more than muttered `Other friends have flown before -\n"
" On the morrow he will leave me, as my hopes have flown before.'\n"
" Then the bird said, `Nevermore.'\n";
std::cout << "Text sample:" << std::endl;;
std::cout << raw_input << std::endl;
// transfer to device
thrust::device_vector<char> input(raw_input, raw_input + sizeof(raw_input));
// count words
int wc = word_count(input);
std::cout << "Text sample contains " << wc << " words" << std::endl;
return 0;
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