LOMHash.c

#include <stdio.h>
typedef unsigned short UINT16;
typedef unsigned char BYTE;
static UINT16 HuffCodeLOM[] = { 0x0001, 0x0000, 0x0002, 0x0009, 0x0006, 0x0005, 0x000d, 0x000b,
                              0x0003, 0x001b, 0x0007, 0x0017, 0x0037, 0x000f, 0x004f, 0x006f,
                              0x002f, 0x00ef, 0x001f, 0x005f, 0x015f, 0x009f, 0x00df, 0x01df,
                              0x003f, 0x013f, 0x00bf, 0x01bf, 0x007f, 0x017f, 0x00ff, 0x01ff };
 
UINT16 HashTable[32] = { [0 ... 31] = 0xffff };
 
BYTE tab[4] = { 0, 4, 10, 19 };
 
UINT16 hash(UINT16 key)
{
  return ((key & 0x1f) ^ (key >> 5) ^ (key >> 9));
}
 
BYTE minihash(UINT16 key)
{
  BYTE h;
  h = (key >> 4) & 0xf;
  return ((h ^ (h >> 2) ^ (h >> 3)) & 0x3);
}
 
void buildhashtable(void)
{
  for (int i = 0; i < 32; i++)
  {
    UINT16 h = hash(HuffCodeLOM[i]);
 
    if (HashTable[h] != 0xffff)
    {
      HashTable[h] ^= (HuffCodeLOM[i] & 0xfe0) ^ 0xfe0;
      HashTable[tab[minihash(HuffCodeLOM[i])]] = i;
    }
    else
    {
      HashTable[h] = i;
      HashTable[h] ^= 0xfe0;
    }
 
    printf("at %d %" PRIu16 "=0x%" PRIx16 "\n", i, h, HashTable[h]);
  }
}
 
BYTE getvalue(UINT16 huff)
{
  UINT16 h = HashTable[hash(huff)];
 
  if ((h ^ huff) >> 5)
  {
    return h & 0x1f;
  }
  else
    return HashTable[tab[minihash(huff)]];
}
 
main()
{
  buildhashtable();
  printf("static UINT16 HuffIndexLOM[32] = {\n");
 
  for (int i = 0; i < 32; i++)
  {
    if (i == 31)
      printf("0x%" PRIx16 " };\n", HashTable[i]);
    else
      printf("0x%" PRIx16 ", ", HashTable[i]);
  }
 
  for (int i = 0; i < 32; i++)
    if (i != getvalue(HuffCodeLOM[i]))
      printf("Fail :( at %d : 0x%04" PRIx16 " got %" PRIu8 "\n", i, HuffCodeLOM[i],
             getvalue(HuffCodeLOM[i]));
 
  return 0;
}