Efficient way to convert a 16-bit short array to a 32-bit int array?

Question

What is the most efficient way to convert an array of unsigned short numbers (16 bits per value) into an array of unsigned ints numbers (32 bits per value)?

Answer 1

Copy it.

unsigned short source[]; // …
unsigned int target[]; // …
unsigned short* const end = source + sizeof source / sizeof source[0];
std::copy(source, end, target);

std::copy internally choses the best copying mechanism for given input types. In this case, however, there’s probably no better way than copying the elements individually in a loop.

Answer 2

Use std::copy in C++:

#include<algorithm> //must include

unsigned short ushorts[M]; //where M is some const +ve integer
unsigned int   uints[N]; //where N >= M
//...fill ushorts
std::copy(ushorts, ushorts+M, uints);

And in C, use manual loop (in fact, you can use manual loop both in C and C++):

int i = 0;
while( i < M ) { uints[i] = ushorts[i]; ++i; }