Editing immediate value

{{title|Immediate Value}}
An '''immediate value''' (or simply an '''immediate''' or '''imm''') is a piece of data that is stored as part of the instruction itself instead of being in a [[memory]] location or a [[register]]. Immediate values are typically used in instructions that [[Load/Store instruction|load]] a value or performs an [[arithmetic instruction|arithmetic]] or a [[logic instruction|logical]] operation on a [[constant]].

== Overview ==
Under most [[instruction set architecture]]s, various instructions can also perform operation on constant values. For example consider an ISA that can add two registers and store the result in a third register:

<pre>add r3, r2, r1       ; r3 = r2 + r1</pre>

The instruction set may also support the common case of adding a constant value (such as in the case of many programming languages that support [[pre-increment operator|++var]]).

<pre>addi r1, r1, 1       ; r1 = r1 + 1</pre>

In the code above, the value <code>1</code> is an immediate value that gets encoded in the <code>add</code> instruction itself.

== Implementation restrictions ==
[[File:MIPS32 add and addi instructions.svg|thumb|right|300px|An encoding comparision between the [[MIPS32]] ADD and ADD Immediate instructions. The immediate value is limited to the 0x00-0xFFFF range.]]
Because the immediate value is packed into the instruction itself certain [[ISA]]s have a restricted range of values that can be used as an immediate value. For example in [[MIPS32]], an immediate value is limited to 16-bits. On some more complex architectures such as [[ARM]], some instructions may accept a 16-bit value, others might accepted a smaller range with a the ability to rotate the bits as desired (see [[LSL - ARM|LSL]]).

[[Category:microprocessor architecture]]
[[Category:Instruction set architecture]]