Generates an entry from the RunList and outputs it in byte order

runlistgen.c

/* INCLUDES *******************************************************************/

#include <stdio.h>
#include <stdlib.h>


/* TYPES **********************************************************************/

#define BYTE   unsigned char
#define PBYTE  BYTE*

#define ULONG  unsigned int
#define PULONG ULONG*


/* BYTES OPERATIONS ***********************************************************/

#define GET_BYTE(val, n) (((val) >> (8*(n))) & 0xFF)

#define GET_BYTE_FROM_END(val, n) (((val) >> (8*(sizeof((val)) - 1 - (n)))) & 0xFF)

#define BSWAP16(val) \
 ( (((val) >> 8) & 0x00FF) | (((val) << 8) & 0xFF00) )

#define BSWAP32(val) \
 ( (((val) >> 24) & 0x000000FF) | (((val) >>  8) & 0x0000FF00) | \
   (((val) <<  8) & 0x00FF0000) | (((val) << 24) & 0xFF000000) )

#define BSWAP64(val) \
 ( (((val) >> 56) & 0x00000000000000FF) | (((val) >> 40) & 0x000000000000FF00) | \
   (((val) >> 24) & 0x0000000000FF0000) | (((val) >>  8) & 0x00000000FF000000) | \
   (((val) <<  8) & 0x000000FF00000000) | (((val) << 24) & 0x0000FF0000000000) | \
   (((val) << 40) & 0x00FF000000000000) | (((val) << 56) & 0xFF00000000000000) )


/* CONSTS *********************************************************************/

#define ENTRY_SIZE 8


/* FUNCTIONS ******************************************************************/

int main()
{
    // Hardcoded values from reality
    ULONG LCN             = BSWAP32(0xC0000);
    BYTE  LCNCutSize      = 3;
    ULONG Clusters        = BSWAP32(0x6340);
    BYTE  ClustersCutSize = 2;
    
    // Run list entry
    PBYTE Entry;
    BYTE  EntryOffset = 0;
    
    BYTE  ClustersOffset = 1;
    BYTE  LCNOffset      = ClustersOffset + ClustersCutSize;
    
    // Allocate memory
    Entry = malloc(ENTRY_SIZE);
    if (!Entry)
    {
        printf("Can't allocate memory for entry\n");
        return 1;
    }
    
    // Fill structure
    
    // Setup header
    Entry[0] = (LCNCutSize << 4) | ClustersCutSize;
        
    // Copy clusters count
    for (EntryOffset = ClustersOffset; EntryOffset < ClustersOffset + ClustersCutSize; EntryOffset++)
    {
        Entry[EntryOffset] = GET_BYTE_FROM_END(Clusters, EntryOffset - ClustersOffset);
    }
    
    // Copy LCN
    for (EntryOffset = LCNOffset; EntryOffset < LCNOffset + LCNCutSize; EntryOffset++)
    {
        Entry[EntryOffset] = GET_BYTE_FROM_END(LCN, EntryOffset - LCNOffset);
    }
    
    // Print entry
    printf("Run List Entry:\n");
    for (EntryOffset = 0; EntryOffset < ENTRY_SIZE; EntryOffset++)
    {
        printf("0x%02hhX ", *(Entry + EntryOffset));
    }
    
    // Free memory
    free(Entry);
    
    return 0;
}