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flat assembler > Macroinstructions > which instruction is quicker?

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CandyMan



Joined: 04 Sep 2009
Posts: 274
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop
which instruction is quicker?
Code:
cmp eax,[0x12345678]    

or
Code:
cmp [0x12345678],eax    

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Post 10 Jul 2018, 09:50
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DimonSoft



Joined: 03 Mar 2010
Posts: 306
Location: Belarus
CandyMan wrote:
which instruction is quicker?
Code:
cmp eax,[0x12345678]    

or
Code:
cmp [0x12345678],eax    

It should be measured but since they differ in a single bit (direction bit) and are converted to a set of RISCy micro-ops by the processor, I guess, the two are equal in speed. For quite strict definitions of equality.
Post 10 Jul 2018, 18:13
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 15912
Location: SDSS J140821.67+025733.2
Measure it. Do you see any difference? If it it really important for you to know which is "quickest" then you will need to measure both variants in your production code to determine which variant works for you.

Other people here could run some test code on their systems, but this is unlikely to give you any useful information about what will happen in your code on your systems.
Post 11 Jul 2018, 01:08
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