The feedback I got on yesterday's article on float-to-int conversion Buy Cafergot Without Prescription, prompted me to look more closely into all the different options MSVC actually gives you for rounding on the x86 architecture. Effects of Cafergot, It turns out that with /fp:fast set it can do one of three things (in addition to the magic-number rounding you can write yourself):


  • By default it will call a function _ftol2_sse, which tests the CPU to see if it has SSE2 functionality, get Cafergot. Cafergot pics, If so, it uses the native SSE2 instruction cvttsd2si, Cafergot images. Where to buy Cafergot, If not, it calls _ftol(), buy Cafergot online cod. Cafergot natural, This is quite slow because it has to perform that CPU test for every single conversion, and because there is that overhead of a function call.

  • With /QIfist specified, ordering Cafergot online, Buy Cafergot without prescription, the compiler simply emits a fistp opcode to convert the x87 floating point register to an integer in memory directly. It uses whatever rounding mode happens to be set in the CPU at the moment.

  • With /arch:SSE2 specified, the compiler assumes that the program will only run on CPUs with SSE2, so it emits the cvttsd2si opcode directly instead of calling _ftol2_sse, Buy Cafergot Without Prescription. Like /QIfist, where can i buy Cafergot online, Cafergot without a prescription, this replaces a function call with a single instruction, but it's even faster and not deprecated, Cafergot class. Doses Cafergot work, As commenter cb points out, the intrinsics also let you specify truncation or rounding without having to fool around with CPU modes.

I raced the different techniques against each other and the clear winner was the function compiled with /arch:SSE2 set, online Cafergot without a prescription. Cheap Cafergot, Thus, if you can assume that your customer will have a CPU with SSE2 enabled, Cafergot without prescription, Cafergot wiki, setting that simple compiler switch will provide you with superior performance for basically no work. The only caveat is that the SSE scalar operations operate at a maximum of double-precision floats, buy Cafergot from mexico, Cafergot no prescription, whereas the old x87 FPU instructions are internally 80-bit — but I've never seen a game application where that level of precision makes a difference.

According to the Steam Hardware Survey, Cafergot street price, Cafergot price, 95% of our customers have SSE2-capable CPUs. The rest are probably not playing your most recent releases anyway, order Cafergot from mexican pharmacy. My Cafergot experience,











Comparison of rounding speeds
8 trials of 1.024*108 floats on a Core2
/fp:fastmagic number/arch:sse2/QIfist
312.944ms184.534ms96.978ms178.732ms
314.255ms182.105ms91.390ms178.363ms
311.359ms181.397ms89.606ms182.709ms
309.149ms181.023ms87.732ms180.485ms
309.828ms181.405ms91.891ms184.785ms
309.595ms176.970ms86.886ms178.501ms
309.081ms179.109ms86.885ms177.811ms
308.208ms176.873ms86.796ms178.051ms

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2 Comments

  1. cb says:

    IMO the biggest win from the sse conversions is that you have direct access to round-to-int and trunc-to-int without changing FPU mode or checking for negatives.

  2. Yuhong Bao says:

    SSE3 have FISTTP which allows direct access to truncation mode when using the x87 stack.

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