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finalfusion specification
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finalfusion specification

Version 0

Goals

finalfusion is a format for storing word embeddings. The goals of the first version of the finalfusion format are:

  1. Easy to parse
  2. Fast to parse
  3. Extensible
  4. Support for:
  • Memory mapping
  • Tokens with spaces
  • Subword units
  • Quantized matrices
  1. Existing embeddings should be convertible

File format

Each finalfusion file consists of a header, followed by chunks. Currently, a finalfusion file must contain the following chunk order:

  1. Optional metadata chunk
  2. Vocabulary chunk
  3. Storage chunk

The permitted chunks may be extended in a future version of the specification. In particular, we would like to make it possible:

  • To have multiple storage chunks per vocabulary.
  • To have multiple vocab-storage pairs.

All data must be in little endian byte order.

Header

The header consists of:

  • 4 bytes of magic: ['F', 'i', 'F', 'u']
  • Format version number: u32
  • Number of chunks: u32 (n_chunks)
  • Chunk identifiers: [u32; n_chunks]

Data types

0: i8
1: u8
2: i16
3: u16
4: i32
5: u32
6: i64
7: u64
8: i128
9: u128
10: f32
11: f64

Chunks

Chunk format

The chunk format is as follows:

  • Chunk identifier: u32
  • Chunk data length: u64
  • Chunk data: n bytes

Simple Vocab

  • Chunk identifier: 1
  • Vocab length: u64 (vocab_len)
  • vocab_len times:
    • word length in bytes: u32 (word_len)
    • word_len times u8.

Finalfusion subword vocab

  • Chunk identifier: 3
  • Minimum n-gram length: u32
  • Maximum n-gram length: u32
  • Bucket exponent: u32
  • Vocab length: u64 (vocab_len)
  • vocab_len times:
    • word length in bytes: u32 (word_len)
    • word_len times u8.

fastText subword vocab

  • Chunk identifier: 7
  • Minimum n-gram length: u32
  • Maximum n-gram length: u32
  • Number of buckets: u32
  • Vocab length: u64 (vocab_len)
  • vocab_len times:
    • word length in bytes: u32 (word_len)
    • word_len times u8.

Explicit n-gram vocab

  • Chunk identifier: 8
  • Minimum n-gram length: u32
  • Maximum n-gram length: u32
  • Vocab length: u64 (vocab_len)
  • vocab_len times:
    • word length in bytes: u32 (word_len)
    • word_len times u8.
  • N-gram vocab length: u64 (n_ngrams)
  • n_ngrams times:
    • n-gram length in bytes: u32 (ngram_len)
    • ngram_len times u8.

Embedding matrix

  • Chunk identifier: 2
  • Shape:
    • Rows: u64 (n_rows)
    • Cols: u32 (n_cols)
  • Data type: u32 (data_type)
  • Padding, such that data is at a multiple of size_of::<data_type>().
  • Data: n_row * n_cols * sizeof(data_type)

Quantized embedding matrix

  • Chunk identifier: 4
  • Use projection (0 or 1): u32
  • Use norms (0 or 1): u32
  • Quantized embedding length: u32 (quantized_len)
  • Reconstructed embedding length: u32 (reconstructed_len)
  • Number of quantizer centroids: u32
  • Quantized matrix rows: u64 (matrix_rows)
  • Quantized matrix type: u32 (quantized_type)
  • Reconstruced matrix type: u32 (reconstructed_type)
  • Padding, such that data is at a multiple of the largest matrix data type.
  • Projection matrix: reconstructed_len x reconstructed_len x sizeof(reconstructed_type)
  • Subquantizers: quantized_len x (reconstructed_len / quantized_len) x sizeof(quantized_type)
  • Norms: matrix_rows x sizeof(reconstructed_type)
  • Quantized embedding matrix: matrix_rows x quantized_len x sizeof(reconstructed_type)

Metadata

  • Chunk identifier: 5
  • UTF8 encoded Metadata in TOML format: chunk_data_len times u8

NdNorms

  • Chunk identifier: 6
  • Number of norms: u64 (n_norms)
  • Data type: u32 (data_type)
  • Padding, such that data is at a multiple of size_of::<data_type>().
  • Data: n_norms * sizeof(data_type)