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История изменений

Исправление beastie, (текущая версия) :

Тогда уж: 

#include <arpa/inet.h>
#include <stdio.h>
#include <stdint.h>

uint32_t
setbyte(uint32_t in, uint8_t val, unsigned int n)
{
        const int bytes = sizeof(uint32_t) / sizeof(uint8_t);
        union {
                uint32_t l;
                uint8_t b[bytes];
        } d;

        if (n >= bytes)
                return in;

        d.l = htonl(in);
        d.b[bytes - n - 1] = val;

        return ntohl(d.l);
}

int
main()
{
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 0));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 1));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 2));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 3));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 4));   // shall fail

        return 0;
}


0x00006141
0x00004100
0x00416100
0x41006100
0x00006100

Исправление beastie, :

Тогда уж: 

#include <arpa/inet.h>
#include <stdio.h>
#include <stdint.h>

uint32_t
setbyte(uint32_t in, uint8_t val, unsigned int n)
{
        const int bytes = sizeof(uint32_t) / sizeof(uint8_t);
        union {
                uint32_t l;
                uint8_t b[bytes];
        } d;

        if (n >= bytes)
                return in;

        d.l = htonl(in);
        d.b[bytes - n - 1] = val;

        return ntohl(d.l);
}

int
main()
{
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 0));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 1));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 2));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 3));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 4));   // shall fail

        return 0;
}


0x00006141
0x00004100
0x00416100
0x41006100

Исходная версия beastie, :

Тогда уж: 

#include <arpa/inet.h>
#include <stdio.h>
#include <stdint.h>

uint32_t
setbyte(uint32_t in, uint8_t val, unsigned int n)
{
        int i = sizeof(uint32_t) / sizeof(uint8_t) - 1 - n;
        union {
                uint32_t l;
                uint8_t b[4];
        } d;

        if (i < 0)
                return in;

        d.l = htonl(in);
        d.b[i] = val;

        return ntohl(d.l);
}

int
main()
{
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 0));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 1));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 2));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 3));
        printf("0x%.8x\n", setbyte(0x6100, 0x41, 4));   // shall fail

        return 0;
}


0x00006141
0x00004100
0x00416100
0x41006100