typedef unsigned char Byte;
...
void ReverseBytes( void *start, int size )
{
Byte *buffer = (Byte *)(start);
for( int i = 0; i < size / 2; i++ ) {
std::swap( buffer[i], buffer[size - i - 1] );
}
}
What this method does right now is it reverses bytes in memory. What I would like to know is, is there a better way to get the same effect? The whole "size / 2" part seems like a bad thing, but I'm not sure.
EDIT: I just realized how bad the title I put for this question was, so I [hopefully] fixed it.
The standard library has a std::reverse function:
#include <algorithm>
void ReverseBytes( void *start, int size )
{
char *istart = start, *iend = istart + size;
std::reverse(istart, iend);
}
A performant solution without using the STL:
void reverseBytes(void *start, int size) {
unsigned char *lo = start;
unsigned char *hi = start + size - 1;
unsigned char swap;
while (lo < hi) {
swap = *lo;
*lo++ = *hi;
*hi-- = swap;
}
}
Though the question is 3 ½ years old, chances are that someone else will be searching for the same thing. That's why I still post this.
If you need to reverse there is a chance that you can improve your algorithms and just use reverse iterators.
If you're reversing binary data from a file with different endianness you should probably use the ntoh* and hton* functions, which convert specified data sizes from network to host order and vice versa. ntohl for instance converts a 32 bit unsigned long from big endian (network order) to host order (little endian on x86 machines).
I would review the stl::swap and make sure it's optimized; after that I'd say you're pretty optimal for space. I'm reasonably sure that's time-optimal as well.
