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SubjectRe: [PATCH] (1/7) entropy, take 2 - log2
Oliver Xymoron wrote:
>
>> +static inline __u32 int_log2_16bits(__u32 word)
> {
> /* Smear msbit right to make an n-bit mask */
> word |= word >> 8;
> word |= word >> 4;
> word |= word >> 2;
> word |= word >> 1;
> - /* Remove one bit to make this a logarithm */
> - word >>= 1;
> - /* Count the bits set in the word */
> - word -= (word >> 1) & 0x555;
> - word = (word & 0x333) + ((word >> 2) & 0x333);
> - word += (word >> 4);
> - word += (word >> 8);
> - return word & 15;
> +
> + return hweight16(word)-1;
> }
> -#endif

I suggest you to use a more efficient version like that below:

static inline int ld2_16(__u16 v)
{
unsigned r = 0;

if (v >= 0x100) {
v >>= 8;
r += 8;
}
if (v >= 0x10) {
v >>= 4;
r += 4;
}
if (v >= 4) {
v >>= 2;
r += 2;
}
if (v >= 2)
r++;
return r;
}


--
Abramo Bagnara mailto:abramo.bagnara@libero.it

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