#include <stdio.h>
#include <string.h>

//comp()
void Compress(unsigned char *szOut, const char *szMessage) {
    unsigned long long nBuffer = 0; //This is enough to store 8 uncompressed characters or 9 compressed. We will only use 8 tho.
    char nBitsInBuffer = 0;
    while (*szMessage != 0) {
        nBuffer |= (unsigned long long)(*szMessage++ & 0x7F) << nBitsInBuffer;
        nBitsInBuffer += 7;
        if (nBitsInBuffer == 7 * 8) { //We have 8 chars in the buffer, dump them
            while (nBitsInBuffer > 0) {
                *szOut++ = nBuffer & 0xFF;
                nBuffer >>= 8;
                nBitsInBuffer -= 8;
            }
            //The following should be redundant, but just to be safe
            nBitsInBuffer = 0;
            nBuffer = 0;
        }
    }
    //Write out whatever is left in the buffer
    while (nBitsInBuffer > 0) {
        *szOut++ = nBuffer & 0xFF;
        nBuffer >>= 8;
        nBitsInBuffer -= 8;
    }
}

//uncomp()
//nCompressedLen is the number of bytes in the compressed buffer.
//NOTE: the compressed buffer does not have a NULL terminating character
void Uncompress(char *szOut, const unsigned char *szCompressed, unsigned nCompressedLen) {
    unsigned long long nBuffer = 0; //This is enough to store 8 uncompressed characters or 9 compressed. We will only use 8 tho.
    char nBitsInBuffer = 0;
    while (nCompressedLen) {
        while (nCompressedLen && nBitsInBuffer < 7 * 8) {
            nBuffer |= (unsigned long long)*szCompressed++ << nBitsInBuffer;
            nBitsInBuffer += 8;
            --nCompressedLen;
        }
        while (nBitsInBuffer > 0) {
            *szOut++ = nBuffer & 0x7F;
            nBuffer >>= 7;
            nBitsInBuffer -= 7;
        }
        //The following should be redundant, but just to be safe
        nBitsInBuffer = 0;
        nBuffer = 0;
    }
}

int main() {
    //char szMessage[] = "\x53\x7F\x63\x4B";
    char szMessage[] = "hello world. this is a compressed long string";
    static const unsigned nCompressedSize = sizeof(szMessage) * 7 / 8; //This does not include the NULL terminating character from the string
    unsigned char pCompressedBytes[nCompressedSize];
    char szUncompressed[sizeof(szMessage)];
    printf("     Message: %s\n", szMessage);
    Compress(pCompressedBytes, szMessage);
    printf("  Compressed: ");
    for (int nByte = 0; nByte < nCompressedSize; ++nByte) {
        printf("%02X ", pCompressedBytes[nByte]);
    }
    printf("\n");
    Uncompress(szUncompressed, pCompressedBytes, nCompressedSize);
    szUncompressed[sizeof(szMessage) - 1] = 0; //We need to terminate the string. The NULL terminator is not stored in the compressed bytes
    printf("Uncompressed: %s\n", szUncompressed);
    //Now just verify that we ended up with the same message we started with
    if (strcmp(szMessage, szUncompressed) == 0) {
        printf("Compression works\n");
    } else {
        printf("Compression failed\n");
    }
    return 0;
}