kaleb@mars.jpl.nasa.gov (Kaleb Keithley) (06/06/90)
I want to create the following bitmask lookup table:
unsigned short masks[] = {
0x0000, 0x0001, 0x0003, 0x0007,
0x000F, 0x001F, 0x003F, 0x007F,
0x00FF, 0x01FF, 0x03FF, 0x07FF,
0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF
};
in a machine independent way.
In /usr/include/values.h, the following are #defined:
#define BITS(type) (BITSPERBYTE * (int)sizeof(type)
#define HIBITS ((short)(1 << BITS(short) - 1))
#define MAXSHORT ((short)~HIBITS)
which are 0x8000 and 0x7FFF respectively on my machine, which happens to
be a Sun Sparc.
It is nearly trivial to do it at run-time, and the above definitely works
on my Sun. Does anyone have any neat trick to generate this table at
compile time in such a way as to be completely machine independent?
adva-thanks-nce
kaleb@thyme.jpl.nasa.gov Jet Propeller Labs
Kaleb Keithley
"So that's what an invisible barrier looks like"kaleb@mars.jpl.nasa.gov (Kaleb Keithley) (06/06/90)
Don't like to follow up my own article, but: In article I wrote: >I want to create the following bitmask lookup table: > unsigned short masks[] = { > 0x0000, 0x0001, 0x0003, 0x0007, > 0x000F, 0x001F, 0x003F, 0x007F, > 0x00FF, 0x01FF, 0x03FF, 0x07FF, > 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF > }; > >in a machine independent way. > >In /usr/include/values.h, the following are #defined: >#define BITS(type) (BITSPERBYTE * (int)sizeof(type) >#define HIBITS ((short)(1 << BITS(short) - 1)) >#define MAXSHORT ((short)~HIBITS) > >which are 0x8000 and 0x7FFF respectively on my machine, which happens to >be a Sun Sparc. > >It is nearly trivial to do it at run-time, and the above definitely works >on my Sun. Does anyone have any neat trick to generate this table at >compile time in such a way as to be completely machine independent? Well, so far I got two answers, one said the above was correct, the other told me to look at X Window Server code. I don't want to belittle the person who told me the above was correct, but... I looked at the MIT server code, and found that it makes two distinctions: If you have a VAX or a 386 then BITMAP_BIT_ORDER is defined as LSBFirst, otherwise it's MSBFirst. Then there are two versions of the table, much like the one I have above, one for MSBFirst, one for LSBFirst. I could do this, and in fact, probably will, but, the question still remains; Is there a way, using the three defined macros, to generate the correct table at compile time? kaleb@thyme.jpl.nasa.gov Jet Propeller Labs Kaleb Keithley "So that's what an invisible barrier looks like"
andre@targon.UUCP (andre) (06/13/90)
In article <3948@jato.Jpl.Nasa.Gov> kaleb@mars.UUCP (Kaleb Keithley) writes: }Don't like to follow up my own article, but: }In article I wrote: }>I want to create the following bitmask lookup table: }> unsigned short masks[] = { }> 0x0000, 0x0001, 0x0003, 0x0007, }> 0x000F, 0x001F, 0x003F, 0x007F, }> 0x00FF, 0x01FF, 0x03FF, 0x07FF, }> 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF }> }; }> }>in a machine independent way. }> }>In /usr/include/values.h, the following are #defined: }>#define BITS(type) (BITSPERBYTE * (int)sizeof(type) }>#define HIBITS ((short)(1 << BITS(short) - 1)) }>#define MAXSHORT ((short)~HIBITS) }>which are 0x8000 and 0x7FFF respectively on my machine, which happens to }>be a Sun Sparc. }>It is nearly trivial to do it at run-time, and the above definitely works ^^^^^^^ ^^^^^^^^ }>on my Sun. Does anyone have any neat trick to generate this table at }>compile time in such a way as to be completely machine independent? If you re-define run-time to be make-time, you can do this easily. Add to your project a small program that will generate the c-code of your correct table and use that to compile the 'big' program. if you decide to put the table in object table.o, executable: $(OBJS) table.o $(CC) -o $@ $(OBJS) table.o table.c: make_table make_table > $@ hope this helps, -- The mail| AAA DDDD It's not the kill, but the thrill of the chase. demon...| AA AAvv vvDD DD Ketchup is a vegetable. hits!.@&| AAAAAAAvv vvDD DD {nixbur|nixtor}!adalen.via --more--| AAA AAAvvvDDDDDD Andre van Dalen, uunet!hp4nl!targon!andre