Bitcoin Cash Specification

Variable Length Integer

A variable-width data format for unsigned integers allowing a more compact representation for smaller values.

Format

Numbers are encoded with the first rule that applies of the following:

  • If the number < 253 (0xFD), store it in 1 byte, left-padded with zeros.
  • If the number fits in 16 bits (but is greater than 252), store it in 3 bytes: a 1-byte value 253 (0xFD) followed by the 2 byte little-endian number.
Byte Index C-Style Calculation
0 0xFD
1 value & 255
2 value >> 8
  • If the number fits in 32 bits (but not 8 or 16), store it in 5 bytes: a 1-byte value 254 (0xFE) followed by the 4 byte little-endian number
Byte Index C-Style Calculation
0 0xFE
1 value & 255
2 (value >> 8) & 255
3 (value >> 16) & 255
4 (value >> 24) & 255
  • If the number fits in 64 bits (but not 8, 16, or 32), store it in 9 bytes: a 1-byte value 255 (0xFF) followed by the 8 byte little-endian number
Byte Index C-Style Calculation
0 0xFF
1 value & 255
2 (value >> 8) & 255
3 (value >> 16) & 255
4 (value >> 24) & 255
5 (value >> 32) & 255
6 (value >> 40) & 255
7 (value >> 48) & 255
8 (value >> 56) & 255