BruteForeCoding.c

//
// Created by tw on 2018/3/1.
//
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>

const uint8_t val8 = 101;
const uint16_t val16 = 10001;
const uint32_t val32 = 100000001;
const uint64_t val64 = 1000000000001L;
const int MESSAGELENGTH = sizeof(uint8_t) + sizeof(uint16_t) + sizeof(uint32_t) + sizeof(uint64_t);

static char stringBuf[BUFSIZ];
char *BytesToDecString(uint8_t *byteArray, int arrayLength) {
    char *cp = stringBuf;
    size_t bufSpaceLeft = BUFSIZ;
    for (int i = 0; i < arrayLength && bufSpaceLeft > 0; i++) {
        int str1 = snprintf(cp, bufSpaceLeft, "%u", byteArray[i]);
        bufSpaceLeft -= str1;
        cp +=str1;
    }
    return stringBuf;
}

int EncodeIntBigEndian(uint8_t dst[], uint64_t val, int offset, int size) {
    for (int i = 0; i < size; i++) {
        dst[offset++] = (uint8_t)(val >> ((size - 1)-i) * CHAR_BIT);
    }
    return offset;
}


uint64_t DecodeIntBigEndian(uint8_t val[], int offset, int size) {
    uint64_t rtn = 0;
    for (int i = 0; i < size; i++) {
        rtn = (rtn << CHAR_BIT) | val[offset+i];
    }
    return rtn;
}

int main(int argc, char *argv[]) {
    uint8_t message[MESSAGELENGTH];

    int offset = 0;
    offset = EncodeIntBigEndian(message, val8, offset, sizeof(uint8_t));
    offset = EncodeIntBigEndian(message, val16, offset, sizeof(uint16_t));
    offset = EncodeIntBigEndian(message, val32, offset, sizeof(uint32_t));
    offset = EncodeIntBigEndian(message, val64, offset, sizeof(uint64_t));

    printf("Encoded message:\n%s\n", BytesToDecString(message, MESSAGELENGTH));

    uint64_t value = DecodeIntBigEndian(message, sizeof(uint8_t), sizeof(uint16_t));
    printf("Decoded 2-byte integer = %u\n", (unsigned int) value);
    value = DecodeIntBigEndian(message, sizeof(uint8_t) + sizeof(uint16_t) + sizeof(uint32_t), sizeof(uint64_t));
    printf("Decoded 8-byte integer - %llu\n", value);

    offset = 4;
    int iSize = sizeof(int32_t);
    value = DecodeIntBigEndian(message, offset, iSize);
    printf("Decoded value (offset %d, size %d) = %lld\n", offset, iSize, value);
    int signedVal = DecodeIntBigEndian(message, offset, iSize);
    printf("...same as signed value %d\n", signedVal);
}