Lolling at programmers, how many ways are there to create a bitmask ? ;) :)
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From: Skybuck Flying on 25 May 2010 09:50 I guess the moral of this story is: Delphi's Overflow/Range checking cannot be trusted at all... I already knew it was bad and missed some cases... but this is getting pretty ridicules! ;) :) It even detects cases/"fake bugs" which seem totally legal and therefore shouldn't have been detected at all ?! wow ?! ;) :) None-the-less it always helps having it on... but it should not be relied on to detect everything. Bye, Skybuck =D
From: Skybuck Flying on 25 May 2010 09:54 My advice will be: Create test programs which test full ranges, and have independent code which test for correct input, correct memory and correct output value's... bit by bit if necessary. Such test programs will catch all cases. I already created such a test program to test my WriteBitfield routines... and the test program proved to be highly successfull and usefull ! =D Bye, Skybuck.
From: Chad on 25 May 2010 11:14 On May 25, 6:54 am, "Skybuck Flying" <IntoTheFut...(a)hotmail.com> wrote: > My advice will be: > > Create test programs which test full ranges, and have independent code which > test for correct input, correct memory and correct output value's... bit by > bit if necessary. > > Such test programs will catch all cases. > > I already created such a test program to test my WriteBitfield routines.... > and the test program proved to be highly successfull and usefull ! =D > <off topic> I can't tell if you are holding a conversation with yourself or if the computers at my job are just doing some kind of wierd filtering that isn't allowing me to see who you are talking to. </off topic>
From: James Harris on 25 May 2010 16:59 On 25 May, 16:51, Andy 'Krazy' Glew <ag-n...(a)patten-glew.net> wrote: .... > When shifts are slow, instruction sets are advised to have instructions to generate bitmasks. > > dest := bitmask(frombit,tobit) > > but even these have 2 6 bit constants (on a 64 bit machine). > > dest := bitmask(bitpos6,len) > > not much better, except for small masks. Right. For what the OP is looking for (rightmost N bits set) a simple lookup table would do. James
From: Skybuck Flying on 25 May 2010 18:32
"James Harris" <james.harris.1(a)googlemail.com> wrote in message news:de444692-fb87-4c7e-9831-c10ae147ab7e(a)v18g2000vbc.googlegroups.com... > On 25 May, 16:51, Andy 'Krazy' Glew <ag-n...(a)patten-glew.net> wrote: > ... >> When shifts are slow, instruction sets are advised to have instructions >> to generate bitmasks. >> >> dest := bitmask(frombit,tobit) >> >> but even these have 2 6 bit constants (on a 64 bit machine). >> >> dest := bitmask(bitpos6,len) >> >> not much better, except for small masks. > > Right. For what the OP is looking for (rightmost N bits set) a simple > lookup table would do. Seems like a waste of L1 data cache to me... it will already be massively used me thinks... I could be wrong though... None the less, the lookup table method is idea another way to do it, I have seen it before... LookupTable : array[0..32] of longword; ^ BitCount goes into it as the index and a longword goes out with a maximum of 32 bits ;) So that'll be number 5. I'll have to consult my "source "databas"" to see who's name it was who's I first saw ! ;) :) Bye, Skybuck. |