chapter1-AppendixA-m2-ziavras

With 2 operands 1 byte for opcode address specifier 1

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Unformatted text preview: is adapted from D. Culler & D. Patterson (UCB) S. Ziavras Basic Variations in Instruction Encoding Variable Fixed Hybrid Some material is adapted from D. Culler & D. Patterson (UCB) S. Ziavras Basic Variations in Instruction Encoding (2) 1. Variable Length – smallest code size – all modes appear with all opcodes 2. Fixed Length – longest code size – operation & mode combined in opcode 3. Hybrid – reduce variability in size & work of variable variability in size work of variable architecture but provide multiple instr. lengths to reduce code size Some material is adapted from D. Culler & D. Patterson (UCB) S. Ziavras Variable Length Encoding Example Intel 80x86 example: “add EAX, 1000(EBX)” • add: 32-bit integer add instr. with 2 operands – 1 byte for opcode • Address specifier: – 1-2 bytes specifying » EAX: source/destination reg. (1st operand) » EBX: base reg. & 1000 (>2^8) displacement (2nd operand) • Total instr. length: 1(EAX)+1...
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