Opcodes
An opcode is a 1-byte FixedUInt that tells the reader what the next expression represents
and how the bytes that follow should be interpreted.
The meanings of each opcode are organized loosely by their high and low nibbles.
| High nibble | Low nibble | Meaning |
|---|---|---|
0x0_ to 0x3_ | 0-F | E-expression with 6-bit address |
0x4_ | 0-F | E-expression with 12-bit address |
0x5_ | 0-F | E-expression with 20-bit address |
0x6_ | 0-8 | Integers from 0 to 8 bytes wide |
9 | Reserved | |
A-D | Floats | |
E-F | Booleans | |
0x7_ | 0-F | Decimals |
0x8_ | 0-C | Short-form timestamps |
D-F | Reserved | |
0x9_ | 0-F | Strings |
0xA_ | 0-F | Symbols with inline text |
0xB_ | 0-F | Lists |
0xC_ | 0-F | S-expressions |
0xD_ | 0 | Empty struct |
1 | Reserved | |
2-F | Structs | |
0xE_ | 0 | Ion version marker |
1-3 | Symbols with symbol address | |
4-6 | Annotations with symbol address | |
7-9 | Annotations with FlexSym text | |
A | null.null | |
B | Typed nulls | |
C-D | NOP | |
E | System symbol | |
F | System macro invocation | |
0xF_ | 0 | Delimited container end |
1 | Delimited list start | |
2 | Delimited S-expression start | |
3 | Delimited struct start | |
4 | E-expression with FlexUInt macro address | |
5 | E-expression with FlexUInt length prefix | |
6 | Integer with FlexUInt length prefix | |
7 | Decimal with FlexUInt length prefix | |
8 | Timestamp with FlexUInt length prefix | |
9 | String with FlexUInt length prefix | |
A | Symbol with FlexUInt length prefix and inline text | |
B | List with FlexUInt length prefix | |
C | S-expression with FlexUInt length prefix | |
D | Struct with FlexUInt length prefix | |
E | Blob with FlexUInt length prefix | |
F | Clob with FlexUInt length prefix |