Author: Dezhi Zhao
Date: 13:14:53 09/27/05
Go up one level in this thread
On September 27, 2005 at 15:42:32, Gerd Isenberg wrote: >On September 27, 2005 at 14:28:42, Dezhi Zhao wrote: > >>On September 27, 2005 at 12:20:27, Bo Persson wrote: >> >>>On September 27, 2005 at 00:56:20, Dezhi Zhao wrote: >>> >>>>VS2005 RC is finally up and running on Win x64 for me. >>>>However I cannot find a template for a simple 64 bit console project. >>>>Or, do I have to use command line? >>>>I want to try some simple int and bit operations and take a look at the x86-64 >>>>asm output. >>>> >>>>Any hints? Thanks >>> >>>Despite the name, you have to choose a Win32 Console Project. Then (if you have >>>installed the 64 bit compiler) you can add an x64 target in the project >>>properties. >>> >>>At least in the beta versions, the installer didn't install the 64 bit compiler >>>unless you explicitly selected it... >>> >>> >>> >>>Bo Persson >> >>Thanks! Your trick works fine for me. >> >>Just took a look at the asm code and it seems to me there are no name for the >>upper 32 bit part of a general 64 bit register. If you want to extract the upper >>32 bits, the compiler generates a right shift operation. > >Yes, same already for x86-32 with 16-bit short values. >32-bit eax and 16-bit ax, but for the upper 16bit you have to shift 16 right ;-) > >Only bytewise registers are accessible in low/high manner from a 64/32/16-bit >register. > You said it! They keep this bad tradition. The problem is shift operations are slow on P4 class processors. Shift is still slow on x86-64, right? >Note that operating on a 32-bit target register implicitely clears the 32-upper >bits. Therefor the hint to use unsigned int as index, because the zero extension >of the required 64-bit address operand register is free, while signed int >requires explicite sign extension. > >Gerd I think this is probally a price for backward compatiblity. I would prefer an explicit extension. This makes the upper 32 bits more useful.
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