This document discusses different methods of instruction interpretation, including basic interpretation using decode and dispatch, threaded interpretation, precoding, and direct threaded interpretation. It focuses on interpreting complex instruction set architectures like IA-32. Interpreting CISC ISAs is challenging due to variable instruction formats, lengths, and field lengths. The interpretation process for IA-32 first decodes the instruction to fill its structure, then dispatches it. Optimizations group common simple instructions that are easily decoded from their first byte. A threaded interpreter for CISC would organize a simple routine for common cases and a centralized routine for complex instructions.

1. INTERPRETATION
BASIC INTERPRETATION
THREADED INTERPRETATION
PRECODING
DIRECT THREADED INTERPRETATION
INTERPRETING COMPLEX INSTRUCTION SET
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2. BASIC INTERPRETATION
• The Decode and Dispatch Method
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3. THREADED INTERPRETATION
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4. PRECODING AND DIRECT THREADED INTERPRETATION
• BASIC PRECODING
 Using intermediate code
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5. DIRECT THREADED INTERPRETATION
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6. INTERPRETING COMPLEX INSTRUCTION SET
 Interpreting a simple instruction set is different from a Complex one
 Interpretation in a CISC instruction set is difficult due to
• Variety of instruction formats
• Variable instruction lengths
• Variable field lengths
INTERPRETATION OF IA-32 ISA
Format of IA-32 Instructions
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7. INTERPRETATION PROCESS IA-32 ISA
 Interpretation of a CISC ISA, particularly IA-32 is straight forward
 The Process contains 2 phases,
• Decoding (fills in instruction structure)
• Dispatch
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8. OPTIMIZATION IN INTERPRETING IA-32 ISA BY COMMON CASES
 In IA-32 ISA there are number of common cases of simple instructions with,
• No prefix bytes
• A Single byte opcode
• Simple operand Specifiers
 These simple instructions may be differentiated from complex ones based on the
first byte information
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9. THREADED INTERPRETATION IN CISC ISA
 To implement a threaded interpreter in CISC ISA, We should organize
• A Simple Decode and Dispatch Routine (for common cases)
• A Centralized Decode and Dispatch Routine (for Complex instructions)
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10. THANK YOU
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