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Need some explanations about this opcode, thanks.

 
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Dr.Disrespect
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PostPosted: Mon Jun 05, 2017 12:10 pm    Post subject: Need some explanations about this opcode, thanks. Reply with quote
The code is like this:
Code:

movd xmm0,[ebp+01]  -- the value in [ebp+01] is "0000004B" in hex, which is "(double)0.01"
add esp,04  -- do something to the stack
cvtdq2ps xmm0,xmm0   -- ????


After "cvtdq2ps xmm0,xmm0", the value in xmm0 is: "75.00 - 0.00 - 0.00 - 0.00". So, "0000004b" is turned into "42960000", but how?

So, what exactly does "cvtdp2ps" do? What's its equivalent in C++ or C#?
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ParkourPenguin
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PostPosted: Mon Jun 05, 2017 12:51 pm    Post subject: Reply with quote
http://x86.renejeschke.de/html/file_module_x86_id_47.html

There are 16 bytes of data in each xmm register. The cvtdq2ps instruction first treats the data in the source operand as 4 4-byte signed integers. Then, it converts those integers to single-precision floats and stores those floats in the respective positions in the destination xmm register.
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Dr.Disrespect
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PostPosted: Mon Jun 05, 2017 3:58 pm    Post subject: Reply with quote
ParkourPenguin wrote:
http://x86.renejeschke.de/html/file_module_x86_id_47.html

There are 16 bytes of data in each xmm register. The cvtdq2ps instruction first treats the data in the source operand as 4 4-byte signed integers. Then, it converts those integers to single-precision floats and stores those floats in the respective positions in the destination xmm register.


Thanks Penguin, your link is very helpful.
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