Revision 12297 changed several bitfields in SPStyle to bool and unsigned int. This means that the size of every SPStyle object will increase by at least 16 bytes. What is the motivation for this change?
Regards, Krzysztof Kosiński
I had a look on the set property of the SPIPaint structure, and I noticed it is only used as a bool, while this property was defined as an unsigned integer. This is not a good programming practice imho. This results in comparing this integer with an a boolean in amongst others desktop-style.cpp line 505. Is this desirable?
Revision 12297 changed several bitfields in SPStyle to bool and unsigned
int. As far as I can see only one field is changed from unsigned integer to bool, so the SPIPaint memory size should decrease. Unless, I overlook something in the code. In that cas, I'd be happy to learn something new. ;-)
Regards, K.
2013/4/22 Krzysztof Kosiński <tweenk.pl@...400...>
Revision 12297 changed several bitfields in SPStyle to bool and unsigned int. This means that the size of every SPStyle object will increase by at least 16 bytes. What is the motivation for this change?
Regards, Krzysztof Kosiński
Precog is a next-generation analytics platform capable of advanced analytics on semi-structured data. The platform includes APIs for building apps and a phenomenal toolset for data science. Developers can use our toolset for easy data analysis & visualization. Get a free account! http://www2.precog.com/precogplatform/slashdotnewsletter _______________________________________________ Inkscape-devel mailing list Inkscape-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/inkscape-devel
2013/4/22 Kris De Gussem <kris.degussem@...400...>:
I had a look on the set property of the SPIPaint structure, and I noticed it is only used as a bool, while this property was defined as an unsigned integer. This is not a good programming practice imho. This results in comparing this integer with an a boolean in amongst others desktop-style.cpp line 505. Is this desirable?
The relevant change is:
=== modified file 'src/style.h' --- src/style.h 2013-04-08 12:16:02 +0000 +++ src/style.h 2013-04-22 12:19:57 +0000 @@ -136,11 +136,11 @@
/// Paint type internal to SPStyle. struct SPIPaint { - unsigned set : 1; - unsigned inherit : 1; - unsigned currentcolor : 1; - unsigned int colorSet : 1; - unsigned int noneSet : 1; + bool set; //todo check if other properties are also booleans + unsigned inherit; + unsigned currentcolor; + unsigned int colorSet; + unsigned int noneSet;
All these properties were declared as unsigned, one-bit bitfields (that's what ": 1" after the name meant), not as full unsigned integers.
See here for details: http://www.tutorialspoint.com/cprogramming/c_bit_fields.htm
Bitfields are slightly slower than unsigned ints, but on modern processors which internally support only aligned adressing modes and emulate non-aligned accesses in microcode, bitfields should have performance equivalent to bools. If there are more than 4 boolean values, as in the case of SPStyle, one-bit bitfields will save space compared to bools.
Comparing one-bit bitfields to booleans is entirely acceptable, since the former can only have the values 0 or 1.
Regards, Krzysztof
Clear. Thanks for the explanation. Reinserted bitfields in r12303
Regards, K.
Op 22/04/2013 17:34, Krzysztof Kosiński schreef:
The relevant change is:
=== modified file 'src/style.h' --- src/style.h 2013-04-08 12:16:02 +0000 +++ src/style.h 2013-04-22 12:19:57 +0000 @@ -136,11 +136,11 @@
/// Paint type internal to SPStyle. struct SPIPaint {
- unsigned set : 1;
- unsigned inherit : 1;
- unsigned currentcolor : 1;
- unsigned int colorSet : 1;
- unsigned int noneSet : 1;
- bool set; //todo check if other properties are also booleans
- unsigned inherit;
- unsigned currentcolor;
- unsigned int colorSet;
- unsigned int noneSet;
All these properties were declared as unsigned, one-bit bitfields (that's what ": 1" after the name meant), not as full unsigned integers.
See here for details: http://www.tutorialspoint.com/cprogramming/c_bit_fields.htm
Bitfields are slightly slower than unsigned ints, but on modern processors which internally support only aligned adressing modes and emulate non-aligned accesses in microcode, bitfields should have performance equivalent to bools. If there are more than 4 boolean values, as in the case of SPStyle, one-bit bitfields will save space compared to bools.
Comparing one-bit bitfields to booleans is entirely acceptable, since the former can only have the values 0 or 1.
Regards, Krzysztof
participants (2)
-
Kris De Gussem -
Krzysztof Kosiński