Bool
A bool is encoded on a single byte, where 0 means false and 1 means true. Other values are invalid.
Fixed-size integral types
| Type | Encoded on N bytes |
|---|---|
int8, uint8 | 1 |
int16, uint16 | 2 |
int32, uint32 | 4 |
int64, uint64 | 8 |
The encoding of all signed integers uses two's complement, the standard representation for signed integers.
Variable-size integral types
A varint32, varuint32, varint62, varuint62 is encoded on 1, 2, 4 or 8 bytes. The least significant 2 bits of the first byte encode the number of bytes used to encode the full value.
| First 2 bits | Number of bytes |
|---|---|
0 | 1 |
1 | 2 |
2 | 4 |
3 | 8 |
The encoding for varuint32 and varuint62 is identical. The value is logically multiplied by 4, or'ed with the value of the first two bits and then stored in the selected number of bytes.
Likewise, the encoding for varint32 and varint62 is identical. The value is logically multiplied by 4, or'ed with the value of the first two bits and then stored in the selected number of bytes.
The value of the first 2 bits indirectly determines the min and max encodable values:
| First 2 bits | Min varint | Max varint | Min varuint | Max varuint |
|---|---|---|---|---|
0 | -2^5 | 2^5 - 1 | 0 | 2^6 - 1 |
1 | -2^13 | 2^13 - 1 | 0 | 2^14 - 1 |
2 | -2^29 | 2^29 - 1 | 0 | 2^30 - 1 |
3 | -2^61 | 2^61 - 1 | 0 | 2^62 - 1 |
In general, a Slice encoder should encode a value on as few bytes as possible. It's however ok for a Slice encoder to encode a value on more bytes than required, and a Slice decoder must always decode such a value properly. For example, 7 is usually encoded on a single byte but can also be encoded on 2, 4 or 8 bytes.
The encoding of varuint62 is identical to the encoding of variable-length integers in QUIC, except for the byte order (QUIC is big-endian, Slice is little-endian).
Floating-point types
A float32 or float64 is encoded on 4 resp. 8 bytes using the binary32 resp. binary64 formats specified by IEEE 754.
String
A string is encoded using UTF-8 as a varuint62 size followed by size UTF-8 bytes. These UTF-8 bytes don't include a BOM. For example, the string "1 μs" is usually encoded as:
0x14 # size 5 encoded on 1 byte0x31 # '1'0x20 # ' '0xCE 0xBC # 'μ'0x73 # 's'The varuint62 size is not necessarily encoded on a single byte. It can be encoded on 1, 2, 4 or 8 bytes. For example:
0x15 0x00 # size 5 encoded on 2 bytesThe size represents the number of UTF-8 bytes in the encoded representation of the string, not the number of characters in this string.