BBC BASIC Programmers' Reference

User Tools

Site Tools

Trace:
aligning_20structures

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
aligning_20structures [2018/04/17 15:01] – Added syntax highlighting tbest3112aligning_20structures [2024/01/05 00:22] (current) – external edit 127.0.0.1
Line 6: Line 6:
 <code bb4w> <code bb4w>
         DIM mystruct{member1, member2, etc, padding%}         DIM mystruct{member1, member2, etc, padding%}
-        !(^mystruct{}+4) = (mystruct{}+4) AND -8+        PTR(mystruct{}) = PTR(mystruct{}) AND -8
 </code> </code>
 When the structure is declared, a dummy member **padding%** is added at the very end; this allows the structure to be moved up in memory by 4 bytes, if necessary, without corrupting subsequent memory contents; //it is vitally important that this member is never written//! The second line adjusts the address of the structure so that it is a multiple of eight.\\ \\  If you want to align the structure at a multiple-of-16 address the padding needs to be 12 bytes in size, most easily arranged by making it an array:\\  When the structure is declared, a dummy member **padding%** is added at the very end; this allows the structure to be moved up in memory by 4 bytes, if necessary, without corrupting subsequent memory contents; //it is vitally important that this member is never written//! The second line adjusts the address of the structure so that it is a multiple of eight.\\ \\  If you want to align the structure at a multiple-of-16 address the padding needs to be 12 bytes in size, most easily arranged by making it an array:\\ 
 <code bb4w> <code bb4w>
         DIM mystruct{member1, member2, etc, padding%(2)}         DIM mystruct{member1, member2, etc, padding%(2)}
-        !(^mystruct{}+4) = (mystruct{}+12) AND -16+        PTR(mystruct{}) = PTR(mystruct{}) AND -16
 </code> </code>
 \\  \\ 
Line 19: Line 19:
         DIM mystruct{member1, member2, etc}         DIM mystruct{member1, member2, etc}
         DIM newdata% DIM(mystruct{})+6         DIM newdata% DIM(mystruct{})+6
-        !(^mystruct{}+4) = (newdata%+7) AND -8+        PTR(mystruct{}) = (newdata%+7) AND -8
 </code> </code>
 Similarly to align it on a multiple-of-16 address:\\  Similarly to align it on a multiple-of-16 address:\\ 
Line 25: Line 25:
         DIM mystruct{member1, member2, etc}         DIM mystruct{member1, member2, etc}
         DIM newdata% DIM(mystruct{})+14         DIM newdata% DIM(mystruct{})+14
-        !(^mystruct{}+4) = (newdata%+15) AND -16+        PTR(mystruct{}) = (newdata%+15) AND -16
 </code> </code>
 Note that you must declare the structure using this method **only once** and not repeat the above code (for example in a loop).\\ \\  If declaring a structure for local use in a procedure or function, use **DIM LOCAL**:\\  Note that you must declare the structure using this method **only once** and not repeat the above code (for example in a loop).\\ \\  If declaring a structure for local use in a procedure or function, use **DIM LOCAL**:\\ 
Line 32: Line 32:
         DIM mystruct{member1, member2, etc}         DIM mystruct{member1, member2, etc}
         DIM newdata% LOCAL DIM(mystruct{})+6         DIM newdata% LOCAL DIM(mystruct{})+6
-        !(^mystruct{}+4) = (newdata%+7) AND -8+        PTR(mystruct{}) = (newdata%+7) AND -8
 </code> </code>
aligning_20structures.1523977269.txt.gz · Last modified: 2024/01/05 00:18 (external edit)