2 May
2015
2 May
'15
8:10 p.m.
Just a curious thought...
If you are using only small values is there really any benefit in using chars
and shorts rather than just using integers everywhere and letting the compiler
sort it out?
Also, would bool actually have an extra cost due to masking needs?
Obviously large blocks of data are a different issue!
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
2 May
2 May
9:07 p.m.
Will Godfrey wrote:
If you are using only small values is there really any
benefit in using chars
and shorts rather than just using integers everywhere and letting the compiler
sort it out?
That depends on the CPU architecture.
Which is why <stdint.h> defines types like int16_fast_t.
Also, would bool actually have an extra cost due to
masking needs?
What masking?
Regards,
Clemens
9:56 p.m.
On Sat, 02 May 2015 21:06:40 +0200
Clemens Ladisch <clemens(a)ladisch.de> wrote:
Will Godfrey wrote:
I thought someone might say that :p
If you are using only small values is there
really any benefit in using chars
and shorts rather than just using integers everywhere and letting the compiler
sort it out?
That depends on the CPU architecture. Which is why <stdint.h> defines types like
int16_fast_t.
Presumably bits have to be masked when being set or read to provide the boolean
action. I wouldn't expect true single bit direct storage to be available.
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
Also, would bool actually have an extra cost due
to masking needs?
What masking? 
10:53 p.m.
On Sat, May 02, 2015 at 08:57:25PM +0100, Will Godfrey wrote:
No, the compiler will use one of the available int sizes (again
depending on CPU) and just test for zero/not-zero. It will not
try to use each bit separately.
For arrays of bool, GCC uses a char for each bool.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
What masking?
Presumably bits have to be masked when being set or read to provide the boolean
action. I wouldn't expect true single bit direct storage to be available.
3 May
3 May
10:02 p.m.
On Sat, 2 May 2015 20:53:15 +0000
Fons Adriaensen <fons(a)linuxaudio.org> wrote:
On Sat, May 02, 2015 at 08:57:25PM +0100, Will Godfrey
wrote:
No, the compiler will use one of the available int sizes (again
depending on CPU) and just test for zero/not-zero. It will not
try to use each bit separately.
For arrays of bool, GCC uses a char for each bool.
Ouch! that could get expensive - although I doubt it will ever be an issue for
me. Certainly worth remembering though.
--
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
What
masking?
Presumably bits have to be masked when being set or read to provide the boolean
action. I wouldn't expect true single bit direct storage to be available.
11:28 p.m.
On Sun, May 03, 2015 at 09:02:55PM +0100, Will Godfrey wrote:
It's a reasonable compromise. Very few application fields use large
arrays of booleans.
Cryptography is one where logic rather than computation is dominant,
but most algorithms are defined on bytes or words anyway. One trick
used there is to run 32 or 64 copies in parallel by using logical
operations on integers. Provided the parallelism can be exploited,
these are often the fastest versions of crypto algorithms.
Languages such as Matlab and numpy can use large multidimensional
boolean arrays. But they always represent a property of the elements
of a numerical array, so that one will take most of the space.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
For arrays of
bool, GCC uses a char for each bool.
Ouch! that could get expensive - although I doubt it will ever be an issue for
me. Certainly worth remembering though. 
9:36 p.m.
* Will Godfrey:
Just a curious thought...
If you are using only small values is there really any benefit in
using chars and shorts rather than just using integers everywhere
and letting the compiler sort it out?
Many languages do not actually support arithmetic on chars and shorts,
but promote them to ints first.
It is usually beneficial to use the smallest possible data type for
arrays because it cuts down memory use and increases the number of
array elements which fit into the CPU caches.
10:03 p.m.
On Sun, 03 May 2015 21:36:25 +0200
Florian Weimer <fw(a)deneb.enyo.de> wrote:
* Will Godfrey:
Currently I work in C and C++. I don't see that changing any time soon. They are
more then enough to keep me occupied!
Just a curious thought...
If you are using only small values is there really any benefit in
using chars and shorts rather than just using integers everywhere
and letting the compiler sort it out?
Many languages do not actually support arithmetic on chars and shorts,
but promote them to ints first. It is usually beneficial to use the smallest possible
data type for
arrays because it cuts down memory use and increases the number of
array elements which fit into the CPU caches.
Good point. I didn't think of that.
--
It wasn't me! (Well actually, it probably was)
... the hard part is not dodging what life throws at you,
but trying to catch the good bits.
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5 participants
participants (5)
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Clemens Ladisch -
Florian Weimer -
Fons Adriaensen -
Will Godfrey -
Will J Godfrey