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   :ihavenomouth: (inginsub@clubcyberia.co)'s status on Monday, 26-Aug-2024 23:28:29 JST :ihavenomouth:
   can I use REX prefixes in 16-bit mode?
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     翠星石 (suiseiseki@freesoftwareextremist.com)'s status on Monday, 26-Aug-2024 23:28:28 JST 翠星石

     in reply to
     @Inginsub No. You can only use r-prefixes in 64-bit mode.
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     :ihavenomouth: (inginsub@clubcyberia.co)'s status on Monday, 26-Aug-2024 23:41:41 JST :ihavenomouth:

     in reply to

     • 翠星石
     @Suiseiseki that sucks
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     翠星石 (suiseiseki@freesoftwareextremist.com)'s status on Monday, 26-Aug-2024 23:41:41 JST 翠星石

     in reply to
     @Inginsub You can use 16 bit registers in 64 bit mode no problem - although that is slower than using 32 bit resisters.
     
     AMD64 uses odd instruction encodings, where 32-bit prefixes for some registers is faster (xor eax,eax is faster than xor rax,rax), although for the extended registers, r9d is slower than r9.