22.6 EBC Instruction Syntax
Most EBC instructions have one or more variations that modify the size of the instruction and/or the behavior of the
instruction itself. These variations will typically modify an instruction in one or more of the following ways:
• The size of the data being operated upon
• The addressing mode for the operands
• The size of index or immediate data
• To represent these variations syntactically in this specification the following conventions are used:
• Natural indexes are indicated with the “Index” keyword, and may take the form of “Index16,” “Index32,” or “In-
dex64” to indicate the size of the index value supported. Sometimes the form Index16|32|64 is used here, which
is simply a shorthand notation for Index16|Index32|Index64. A natural index is encoded per Index Encoding is
resolved at runtime.
• Immediate values are indicated with the “Immed” keyword, and may take the form of “Immed16,” “Immed32,”
or “Immed64” to indicate the size of the immediate value supported. The shorthand notation Immed16|32|64 is
sometimes used when different size immediate values are supported.
• Terms in brackets [ ] are required.
• Terms in braces { } are optional.
• Alternate terms are separated by a vertical bar |.
• The form R1 and R2 represent Operand 1 register and Operand 2 register respectfully, and can typically be any
VM general-purpose register R0-R7.
• Within descriptions of the instructions, brackets [ ] enclosing a register and/or index indicate that the contents of
the memory pointed to by the enclosed contents are used.

22.5 EBC Instruction Operands
...
INSTRUCTION Operand1, Operand2
...
Typically, instruction operands will be one of the following:
• Direct
• Indirect
• Indirect with index
• Immediate

22.5.2 Indirect Operands
When an indirect operand is specified, a VM register contains the address of the operand data. This is sometimes
referred to as register indirect, and is indicated by prefixing the register operand with “@.”

1.9.5 Pseudo-Code Conventions
Pseudo code is presented to describe algorithms in a more concise form. None of the algorithms in this document are
intended to be compiled directly. The code is presented at a level corresponding to the surrounding text.
In describing variables, a list is an unordered collection of homogeneous objects. A queue is an ordered list of homo-
geneous objects. Unless otherwise noted, the ordering is assumed to be FIFO.
Pseudo code is presented in a C-like format, using C conventions where appropriate. The coding style, particularly
the indentation style, is used for readability and does not necessarily comply with an implementation of the UEFI
Specification.