Does my AMD-based machine use little endian or big endian?

All x86 and x86-64 machines (which is just an extension to x86) are little-endian.

You can confirm it with something like this:

#include <stdio.h>
int main() {
    int a = 0x12345678;
    unsigned char *c = (unsigned char*)(&a);
    if (*c == 0x78) {
       printf("little-endian\n");
    } else {
       printf("big-endian\n");
    }
    return 0;
}