rle.c

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

int encode_rle(unsigned char *src,int size,unsigned char *dst)
{
	int stat[256];
	int i,tag,sym,sym_prev,len,ptr;
	//	count how often each byte is used , to find an unused byte
	memset(stat,0,sizeof(stat));
	for(i=0;i<size;++i) ++stat[src[i]];
	//	find a free one
	tag=-1;
	for(i=0;i<256;++i)
	{
		if(!stat[i])
		{
			tag=i;
			break;
		}
	}
	//	if we fail , just fall out, I've not hit this yet  
	if(tag<0) return -1;

	ptr=0;
	len=1;
	sym_prev=-1;
	//	1st byte is the tag 
	//	
	dst[ptr++]=tag;
	for(i=0;i<size;++i)
	{
		sym=src[i];

		if(sym_prev!=sym||len>=255||i==size-1)
		{
			if(len>1)
			{
				if(len==2)
				{
					dst[ptr++]=sym_prev;
				}
				else
				{
					dst[ptr++]=tag;
					dst[ptr++]=len;
				}
			}

			dst[ptr++]=sym;
			sym_prev=sym;
			len=1;
		}
		else
		{
			++len;
		}
	}

	dst[ptr++]=tag;	//end of file marked with zero length rle
	dst[ptr++]=0;
	return ptr;
}

int main(int argc,char *argv[])
{
unsigned char buffer[65536];	
unsigned char obuffer[65536];	
int len=0;
int size;
	FILE *file=fopen(argv[1],"rb");
	if(file)
	{
		fseek(file,0,SEEK_END);
		size=ftell(file);
		fseek(file,0,SEEK_SET);
		fread(&buffer[0x00], 1, size, file);
		fclose(file);
	}
	len = encode_rle(buffer,size,obuffer);
	FILE *fou = fopen(argv[2],"wb");
	fwrite(obuffer,len,1,fou);
	fclose(fou);
	printf("original %d packed %d\n",size,len);
	return 0;
}

unpack.mfk

void vunrle(word dest,pointer source) {
word index 
byte counter
byte i 
byte value 
byte tag
byte itag
  //  vram address 
	vout(VDP_CTRL,dest.lo)
	vout(VDP_CTRL,dest.hi)

	//	tag byte is the 1st byte in the data stream 
	tag = source[0]
	index = 1
	while true {
		value = source[index]
		index+=1
		itag = source[index]
		counter = 0
		if itag==tag {
			index+=1
			counter= source[index]
			if counter == 0 {
				return
			}
			index+=1
		}
    //  just write the byte out
		if counter==0 {
			vout(VDP_DATA,value)
		}
		else {
    //  write a run of them out
			for i,0,until,counter {
				vout(VDP_DATA,value)
			}
		}
	}
}