While reading the Intel 64 and IA-32 Architectures Software Developer’s Manual, the operation section for the LEA instruction (load effective address) uses a calculation called EffectiveAddress(SRC) which is not defined anywhere else.
What is the definition of effective address and what does EffectiveAddress(SRC) do?
Section 3.7.5 (Specifying an Offset) of the same document states:
The offset part of a memory address can be specified directly as a static value (called a displacement) or through an address computation made up of one or more of the following components:
- Displacement — An 8-, 16-, or 32-bit value.
- Base — The value in a general-purpose register.
- Index — The value in a general-purpose register.
- Scale factor — A value of 2, 4, or 8 that is multiplied by the index value.
The offset which results from adding these components is called an effective address. Each of these components can have either a positive or negative (2s complement) value, with the exception of the scaling factor.
EffectiveAddress calculates an effective address using:
Base + (Index*Scale) + Displacement