Instruction set reference

Instructions are variable length. Each instruction starts with an opcode of one or more bytes, followed by zero or more arguments. Some instructions have a variable number of arguments, that is, their argument count depends on the value of an earlier argument. Usually this is only used to form instruction groups. In the reference implementation, each one- or two-byte opcode corresponds to one function. We may treat instruction groups with two-byte fixed opcodes and a function selection argument as multiple instructions, depending on how much functionality/code is shared.

The following argument types are supported:

• uchar: An unsigned 8-bit integer. Usually used for selecting one instruction from an instruction group.
• ushort: An unsigned 16-bit integer. Usually used to reference string, label or return address IDs.
• expr: An expression.

How to read this

Each instruction definition in this section contains a quick-reference header providing:

• The instruction name, in the upper left.
• The instruction opcode(s), in the upper right.
• A short summary of the instruction's function, in the middle.
• A list of arguments, at the bottom. Note that, as argument count is variable, this only includes the required arguments.

Note: Instruction names are defined by us and likely do not match official names. While we have looked at SRC/SCS source code, and our naming scheme is inspired by it, we cannot make every name match (as the instruction set differs between games), and so we do not try.