libevent-bswap.c

#include <limits.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
    const char * arg = argv[1];
    uint64_t in_host = strtoll(arg, NULL, 16);
    uint64_t in_network = __bswap_64(in_host);
    uint64_t out_host = 0;

    unsigned char * data;

    data = (unsigned char *)&in_network;
    for (ssize_t i = sizeof(uint64_t) * (CHAR_BIT - 1), pos = 0; i >= 0; i -= CHAR_BIT) {
        /* out_host |= (uint64_t)(data[pos++] & 0xff) << i; */
        /* out_host |= (uint64_t)((unsigned char)data[pos++]) << i; */
        printf("data[i] = %x\n", data[pos]);
        out_host |= (uint64_t)data[pos++] << i; // bug
        printf("out_host = 0x%lx\n", out_host);
    }

    uint64_t out_network;
    data = (unsigned char *)&out_network;
    for (ssize_t i = sizeof(uint64_t) * (CHAR_BIT - 1), pos = 0; i >= 0; i -= CHAR_BIT) {
        data[pos++] = out_host >> i & 0xFFu;
    }

    printf("arg=%s, in_host=0x%lx, in_network=0x%lx, out_host=0x%lx, out_network=0x%lx\n", arg, in_host, in_network, out_host, out_network);
    return 0;
}

$ /tmp/le-test1 deadbeaf | grep 0xafbeadde00000000
arg=deadbeaf, in_host=0xdeadbeaf, in_network=0xafbeadde00000000, out_host=0xdeadbeaf, out_network=0xafbeadde00000000