FixedHash

FixedHash

File format
Endianness	little
Version	1
This article is about the file format in general. For actual values, check the game RomFS.

FixedHash is a custom Grezzo format for serializing hash tables that map string keys to arbitrary binary blobs.

Hash function

String keys are hashed using the following hash function:

u32 Hash(const char* key) {
  u32 hash = 0;
  while (*key) {
    hash ^= *key++ + (h >> 2) + (h << 5);
  }
  return hash;
}

Format

Offset	Type	Description
0x0	u8	Magic (must be 0x3D)
0x1	u8	Version (must be 1)
0x2	u16	Number of hash table buckets (N)
0x4	u16	Number of child FixedHash nodes
0x6	u16	Padding? [check]
0x8	u32[N + 1]	Offsets to the first entry in each bucket (relative to the Entries section) 0xFFFFFFFF for empty buckets.
X = (0x8 + 4*(N+1) + 3) & -8	u64	Entries section size
X + 8	Entry[...]	Entries
Y = align(X + entries section size, 8)	u64	Entry offsets section size
Y + 8	u32[...]	Entry offsets (relative to the Entries section)
Z = align(Y + entry offset section size, 8)	u64	Data section size
Z + 8	any	Data
A = align(Z + data section size, 4)	u32	Names section size
A + 4	C strings	Names

Entry

Offset	Type	Description
0x0	u16	Node index if this describes a FixedHash child node (if so, it must be <= 0xFFED) Otherwise, must be >= 0xFFF0 for non-node data.
0x2	u16	Name offset (relative to the Name section)
0x4	u32	Name hash
0x8	u32	Next entry offset (relative to the Entries section) for hash table collision resolution. 0xFFFFFFFF if there is no other entry in the bucket.
0xC	u32	Data offset (relative to the Data section) For non-node data, the data size is stored at offset+0 as a u64 and the actual data is at offset+8.