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What was the main reason to add REX prefix for 64bit? Why not create longer register bits to hold 16 registers? Was it for easier binary to binary transformatio
by flamedoge 10y ago
What was the main reason to add REX prefix for 64bit? Why not create longer register bits to hold 16 registers? Was it for easier binary to binary transformation?
- pcwalton 10y agoBecause AMD was deathly afraid of AMD64 going the way of Itanium. So they went out of their way to make their architecture as similar to 32-bit x86 as possible, right down to reusing the encoding. They also probably figured that they could reuse decoding logic.