john13@garfield.UUCP (John Russell) (01/12/88)
If I want to create an auto-initialized array of UBYTES, and then later access each 4 bytes as a longword, can I ensure that the array is longword aligned in some portable way (eg by placing it immediately after some other 32-bit global variable)? Will some compilers re-arrange declared storage behind my back? John
ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) (01/13/88)
In article <4366@garfield.UUCP> john13@garfield.UUCP (John Russell) writes: >If I want to create an auto-initialized array of UBYTES, and then later >access each 4 bytes as a longword, can I ensure that the array is longword >aligned in some portable way (eg by placing it immediately after some other >32-bit global variable)? Why don't you simply create it as an array of longwords, then access it as bytes with a coerced pointer? ULONG foo[] = { 1, 2, 3, 4, 5, ...n }; bar() { UBYTE *bp; bp = (UBYTE *) foo; . . . } No muss, no fuss, guaranteed alignment (if the compiler supports it). _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ Leo L. Schwab -- The Guy in The Cape ihnp4!ptsfa -\ \_ -_ Recumbent Bikes: dual ---> !{well,unicom}!ewhac O----^o The Only Way To Fly. hplabs / (pronounced "AE-wack") "Work FOR? I don't work FOR anybody! I'm just having fun." -- The Doctor
cmcmanis%pepper@Sun.COM (Chuck McManis) (01/13/88)
In article <4366@garfield.UUCP> john13@garfield.UUCP (John Russell) writes:
!>If I want to create an auto-initialized array of UBYTES, and then later
!>access each 4 bytes as a longword, can I ensure that the array is longword
!>aligned in some portable way (eg by placing it immediately after some other
!>32-bit global variable)? Will some compilers re-arrange declared storage
!>behind my back?
The system call AllocMem() will guaruntee that the data is longword aligned.
The only hitch being that you have to remember to free it before you exit.
--Chuck McManis
uucp: {anywhere}!sun!cmcmanis BIX: cmcmanis ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.bobb@tekfdi.TEK.COM (Robert Bales) (01/14/88)
In article <4366@garfield.UUCP> john13@garfield.UUCP (John Russell) writes: >If I want to create an auto-initialized array of UBYTES, and then later >access each 4 bytes as a longword, can I ensure that the array is longword >aligned in some portable way (eg by placing it immediately after some other >32-bit global variable)? Perhaps by using a union containing the array of UBYTES and a longword. Such a technique is illustrated on page 173-174 of K&R. I say "perhaps" because I don't know if a union can be auto-initialized. (A quick search of K&R didn't yield the answer.) "See you at AmiExpo" Bob Bales Tektronix, Inc. I help Tektronix make their instruments. They don't help me make my opinions.
john13@garfield.UUCP (John Russell) (01/15/88)
In article <4974@well.UUCP> ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab) writes: >In article <4366@garfield.UUCP> john13@garfield.UUCP (John Russell) writes: [ accessing bytes in an array as longs ] > Why don't you simply create it as an array of longwords, then access >it as bytes with a coerced pointer? >ULONG foo[] = { 1, 2, 3, 4, 5, ...n }; Um, not ideal since the data makes much more sense as bytes -- it's bitmapped definitions for the character set, and it helps to be able to check the accuracy of the definitions visually (or at least it did when I was debugging that section). I like to keep data in the most easily-interpreted form possible, such as the binary-constant macros that I posted and use for things like single-plane gadgets. John PS I ended up using a union, 8 bytes or 2 longs. -- "Let's get those teabags outta here and replace them with some REAL Americans!" -- (Canadian) Paul Schaeffer has members of the British nobility physically ejected from the Late Night crowd