his instruction can be used with a LOCK prefix to allow the instruction to be executed atomically.</p>
<p>In 64-bit mode, DEC r16 and DEC r32 are not encodable (because opcodes 48H through 4FH are REX prefixes). Otherwise, the instruction’s 64-bit mode default operation size is 32 bits. Use of the REX.R prefix permits access to additional registers (R8-R15). Use of the REX.W prefix promotes operation to 64 bits.</p>
<p>See the summary chart at the beginning of this section for encoding data and limits.</p