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AnswerRe: C++ programming Pin
Victor Nijegorodov15-May-21 3:50
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Richard MacCutchan15-May-21 6:15
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QuestionMessage Closed Pin
15-May-21 1:38
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AnswerRe: cross platform dynamic dll Pin
Richard MacCutchan14-May-21 22:21
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GeneralRe: cross platform dynamic dll Pin
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QuestionC++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
charlieg14-May-21 11:01
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AnswerRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
k505414-May-21 12:02
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GeneralRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
harold aptroot14-May-21 18:58
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k5054 wrote:
I think you need to be careful with #pragma pack. X86-64 doesn't seem to have a problem accessing unaligned data, but I assume its slower to do so than correctly aligned data.
A bit, on average, but not due to mere misalignment itself. There is a small penalty for crossing cache line boundaries and a different one (~85 cycles on Haswell, even more on Core2, not so much on AMD processors or Skylake and newer) for crossing 4K boundaries. That makes random unaligned loads and stores a bit slower on average, since some of them will cross those boundaries, but it doesn't make all of them slower and the impact is averaged out. Usually the addresses wouldn't really be random of course, so you could run into some situation where it keeps hitting a bad case, which would amplify the problem.

There are various other caveats..

Of course, avoiding unaligned operations avoids the whole issue.
GeneralRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
charlieg16-May-21 3:46
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GeneralRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
k505416-May-21 4:51
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GeneralRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
charlieg16-May-21 6:05
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GeneralRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
Richard MacCutchan16-May-21 21:21
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GeneralRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
charlieg17-May-21 1:37
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GeneralRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
Bram van Kampen10-Jun-21 14:33
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AnswerRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
Richard MacCutchan14-May-21 22:19
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AnswerRe: C++ Structure layouts - how to determine padding and what not - VS2008 but it's a general question Pin
charlieg16-May-21 1:57
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QuestionHow to migrate qt creator project (that doesn't need qt) to visual studio Pin
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AnswerRe: How to migrate qt creator project (that doesn't need qt) to visual studio Pin
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QuestionQuestion Arduino programming + joystick + bulbs Pin
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QuestionWaitForMultipleObjects getting access violation in Worker Thread Pin
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