dealing with endianness in c++

Question

I am working on translating a system from python to c++. I need to be able to perform actions in c++ that are generally performed by using Python\'s struct.unpack

Answer 1

This falls in the realm of bit twiddling.

for (i=0;i

where mask == (sizeof type -1) if the stored and native endianness differ.

With this technique one can convert a struct to bit masks:

 struct foo {
    byte a,b;       //  mask = 0,0
    short e;        //  mask = 1,1
    int g;          //  mask = 3,3,3,3,
    double i;       //  mask = 7,7,7,7,7,7,7,7
 } s; // notice that all units must be aligned according their native size

Again these masks can be encoded with two bits per symbol: (1<, meaning that in 64-bit machines one can encode necessary masks of a 32 byte sized struct in a single constant (with 1,2,4 and 8 byte alignments).

unsigned int mask = 0xffffaa50;  // or zero if the endianness matches
for (i=0;i<16;i++) { 
     dst[i]=src[i ^ ((1<<(mask & 3))-1]; mask>>=2;
}