On Fre, 2012-09-14 at 08:30 -0400, Jim Rees wrote:
> Bernd Petrovitsch wrote:
[...]
> A pure K&R-C version would use a string:
> ---- snip ----
> #define base10len(i) "\0x1\0x3\0x5\0x8\0x0A\0x0D\0x0F\0x11\0x14"[sizeof(i)]
> ---- snip ----
> (if I converted them properly into hexadecimal) and that gives a "char"
> which is happily promoted to whatever one needs in that place.
>
> 1. That may give you a signed char on some architectures, which is not what
> you want (although it doesn't matter since the values are all < 128)
And it depends on compiler options BTW.
But we can easily cast it:
#define base10len(i) ((unsigned char)"\x1\x3\x5\x8\xA\xD\xF\x11\x14"[sizeof(i)])
> 2. If you put this in a .h, you'll get multiple copies of the array
That depends on the compiler.
> 3. No bounds checking (but in ninja K&R style you never check bounds)
Well, I assumed that we don't use VLAs as parameter for the sizeof() so
the value is compile time known and the better C compilers can check it.
And then, there is no reason to store the string as such too.
[....]
> Pure K&R:
We can (and should) make it "const" too.
> base10.h:
> extern unsigned char base10len_vals[];
extern const unsigned char base10len_vals[];
> #define base10len(i) (base10len_vals[sizeof(i)])
>
> base10.c:
> unsigned char base10len_vals[] = {1,3,5,8,10,13,15,17,20};
const unsigned char base10len_vals[] = {1,3,5,8,10,13,15,17,20};
> But I still like my way better.
The 8 wasted bytes probably do not matter ....
Bernd
--
Bernd Petrovitsch Email : be...@petrovitsch.priv.at
LUGA : http://www.luga.at
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