Run Length Encoding

rlencoding.cpp

/**
    @file rlencoding.cpp
    @breif Run Length Encode and Decode
    @author Natesh Narain
*/

#include "rlencoding.h"

int rlencode(uint8_t *inBuffer, int inLen, uint8_t *outBuffer, int outLen, uint8_t esc)
{
    int i, outIdx = 0;

    uint8_t current = inBuffer[0];
    uint8_t count = 0;

    for(i = 0; i < inLen; ++i){

        if(outIdx >= outLen) return outIdx;

        // count the number of the current character
        if(current == inBuffer[i] || count == 0xFF){
            count++;
        }
        else{
            // greater than 2 encoding
            if(count > 2){
                if(current != esc){
                    outBuffer[outIdx++] = esc;
                    outBuffer[outIdx++] = count;
                    outBuffer[outIdx++] = current;
                }
                else{
                    // cases where we are encoding the esc character
                    if(count == 2){
                        outBuffer[outIdx++] = esc;
                        outBuffer[outIdx++] = 0x01;
                    }
                    else{
                        outBuffer[outIdx++] = esc;
                        outBuffer[outIdx++] = 0x02;
                        outBuffer[outIdx++] = count;
                    }
                }
            }
            // 2 or less encoding (2 or 1)
            else{
                if(current == esc){
                    outBuffer[outIdx++] = esc;
                    outBuffer[outIdx++] = count - 1; // [ESC $00] is 1 ESCs, [ESC $01] is 2 ESCs
                }
                else{
                    if(count == 2){
                        outBuffer[outIdx++] = current;
                        outBuffer[outIdx++] = current;
                    }
                    // must be 1
                    else{
                        outBuffer[outIdx++] = current;
                    }
                }
            }
            // change to the different character
            current = inBuffer[i];
            count = 1;
        }
    }

    return outIdx;
}

int rldecode(uint8_t* inBuffer, int iLen, uint8_t* outBuffer, int max, uint8_t esc)
{
    int i, j, outIdx = 0;
    for(i = 0; i < iLen; ++i)
    {
        // escape sequence found
        if(inBuffer[i] == esc){

            uint8_t count = inBuffer[++i];

            if(count > 2){
                uint8_t byte = inBuffer[++i];

                for(j = 0; j < count; j++){
                    outBuffer[outIdx++] = byte;
                }
            }
            else if(count == 2){
                uint8_t realCount = inBuffer[++i];

                for(j = 0; j < realCount; ++j){
                    outBuffer[outIdx++] = esc;
                }
            }
            else if(count == 1){
                outBuffer[outIdx++] = esc;
                outBuffer[outIdx++] = esc;
            }
            else if(count == 0){
                outBuffer[outIdx++] = esc;
            }

        }
        else{
            outBuffer[outIdx++] = inBuffer[i];
        }
    }

    return outIdx;
}