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cembeddedboolean
Alphaneo
Alphaneo

Reputation: 12539

BOOL definition

Whenever BOOL datatype is not readily predefined, I used to boolean with the following definition,

typedef unsigned char BOOL;

(Owing to memory usage).

I realized it may be better to use native bus width for performance reasons. For example, for a 32 bit processor it can be

typedef unsigned int BOOL;

Now, what will happen for the 64 bit processor, if I still want to define BOOL for the native bus width.

Upvotes: 2

Views: 5728

Answers (10)

philant
philant

Reputation: 35816

Never speculate on performances, measure. Measuring, will give the definitive answer on what is better - and remember this may change at each new compiler version, system upgrade ...

Also one day you might need an array of boolean, in which case using the processor word for a bool can not be the best solution.

Upvotes: 9

dmityugov
dmityugov

Reputation: 4478

int_fast8_t from stdint.h should be a good choice

Upvotes: 0

vitaly.v.ch
vitaly.v.ch

Reputation: 2532

optimal for most platform

typedef enum { FALSE = 0, TRUE = 1, } BOOL;

Upvotes: 2

TrayMan
TrayMan

Reputation: 7445

At least x86 and ARM are capable of loading and storing a byte to and from a 32-bit register without any penalties, so there really is no performance impact for using char. I'm not entirely sure, but I'd bet that x86-64 has such instructions too. (Of course x86 and x86-64 can handle 8-bit values directly in registers too.).

So the only concern might be about memory layout. Of course the compiler aligns everything, so most of the time, char values in structs get padded, unless they are right next to each other, then you might actually save a few bytes of space and get a slightly better cache performance. If you have huge arrays of BOOLs and memory is a concern, you should bit pack them anyway.

In any case, it's a non-issue. Why don't you try running a program compiled both ways and see, if there's any significant impact on performance or memory usage. If you find that there is, you can buy yourself a beer and pretend it's from me.

Upvotes: 2

Arafangion
Arafangion

Reputation: 11910

Using a char might be slower than using an integer.

Upvotes: 0

Judge Maygarden
Judge Maygarden

Reputation: 27583

Why don't you use the bool type in stdbool.h?

Upvotes: 5

lakshmanaraj
lakshmanaraj

Reputation: 4175

I would recommend to use preprocessor.

 #ifndef BOOL 
   #ifdef ILP32
     #define BOOL uint32_t
   #endif
   #ifdef LP64
     #define BOOL uint64_t
   #endif
 #endif

Upvotes: 3

TofuBeer
TofuBeer

Reputation: 61526

size_t

Upvotes: 4

Assaf Lavie
Assaf Lavie

Reputation: 75973

Well you could always define the typedef to long long or something, but I'm actually not sure this is something people do for some reason. (you could probably also do a conditional definition based on sizeof(int*) or something like that).

Upvotes: 0

MarkusQ
MarkusQ

Reputation: 21950

I wouldn't worry about the native bus width so much as an efficient width (that was your goal, right)? On pretty much any machine, any decent c compiler will compile unsigned int to a reasonably efficient width, so you're good to go.

Upvotes: 13

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