swapping bytes in float array

Question

I am currently working on a binary file format where the data is represented as an array of floats and the data is always supposed to be written with the little endian representation. So, currently I do something as follows:

float * swapped_array = new float[length_of_array];

for (int i = 0; i < length_of_array; ++i) {
    swapped_array[i] = swap_float(input_array[i]);
}

Here the swap_float swaps the four bytes of the floating point value. Now, I was wondering if there is a way to do this in a cross platform way without iterating using this for loop and making it more computationally efficient.

Duplicate question (no research): http://stackoverflow.com/questions/2782725/converting-float-values-from-big-endian-to-little-endian — Weather Vane, Dec 15 '14 at 19:40
http://www.boost.org/doc/libs/develop/libs/endian/doc/index.html — IdeaHat, Dec 15 '14 at 19:42
Also possible duplicate of this question: http://stackoverflow.com/questions/8784082/how-to-do-serialization-of-float-numbers-on-network — Julian, Dec 15 '14 at 19:45
It is not a duplicate as I want to do it on arrays rather than single floats... — Luca, Dec 15 '14 at 19:50

score 2 · Accepted Answer · answered Dec 15 '14 at 19:43

2

Looks to me you can swap the bytes by using some pointer arithmetic:

byte mem;
byte* first = (byte*) floatpointer;
mem = *first;
*first = *(first+0x03);
*(first+0x03) = mem;
first++;
mem = *first;
*first = *(first+0x01);
*(first+0x01) = mem;

answered Dec 15 '14 at 19:43

Willem Van Onsem

397,926
29
362
485

Should I not take the size of float on the given platform into account somehow... I think this assumes that the float is 4 bytes? – Luca Dec 15 '14 at 19:50
Well it is possible, will do a small rewrite. – Willem Van Onsem Dec 15 '14 at 19:52
Yeah, I will get it sorted. Thanks. – Luca Dec 15 '14 at 19:54

swapping bytes in float array

1 Answers1