> Ohh... I used to think I know something about optimization. I tried build
> Rasmus' 'find_last_bit' against mine on MIPS, and found that sizes are as
> 268 vs 320 bytes. I think the best version is suggested by George, both
> readable, and effective. What about using it? If no objections, I'll
>
On Fri, Feb 13 2015, "George Spelvin" wrote:
>> the main loop is 20--3b. The test instruction at 2e seems to be
>> redundant. The same at 37: the sub instruction already sets plenty of
>> flags that could be used, so explicitly comparing %rbx to -1 seems
>> redundant.
>
> Er... I think you hand-e
> That, and if the compiler was smart enough, the AND should actually be
> free (at least on x86), since it can replace a test instruction. [1]
Ah, right, x86 loads don't set the flags, so you need a TEST
instruction anyway. So the AND is free!
Of course, not all the world's an x86. But load/st
On Thu, Feb 12 2015, "George Spelvin" wrote:
>> Rasmus, your version has ANDing by mask, and resetting the mask at each
>> iteration
>> of main loop. I think we can avoid it. What do you think on next?
>
> Yes, that's basically what I proposed (modulo checking for zero size and
> my buggy LAST_W
> Rasmus, your version has ANDing by mask, and resetting the mask at each
> iteration
> of main loop. I think we can avoid it. What do you think on next?
Yes, that's basically what I proposed (modulo checking for zero size and
my buggy LAST_WORD_MASK).
But two unconditional instructions in the l
On 09.02.2015 14:53, Rasmus Villemoes wrote:
> [Yury, please do remember to Cc everyone who has previously
> participated]
>
> On Mon, Feb 09 2015, "George Spelvin" wrote:
>
>> Two more comments on the code. Two minor, but one that
>> seems like a bug, so for now, it's
>>
>> Nacked-by: George Sp
[for some reason google decided to put this in my spam folder, hrmpf]
On Mon, Feb 09 2015, "George Spelvin" wrote:
> Sorry, I screwed up the bit-twiddling while messing with various options.
> I was trying to get size == 32 to work; that should have been:
>
>> tmp &= (2UL << ((size-1) % BIT
Sorry, I screwed up the bit-twiddling while messing with various options.
I was trying to get size == 32 to work; that should have been:
> tmp &= (2UL << ((size-1) % BITS_PER_LONG)) - 1; /* Mask last word */
And you're right that LAST_WORD_MASK is a good wrapper.
Vasrious working solutions
[Yury, please do remember to Cc everyone who has previously
participated]
On Mon, Feb 09 2015, "George Spelvin" wrote:
> Two more comments on the code. Two minor, but one that
> seems like a bug, so for now, it's
>
> Nacked-by: George Spelvin
>
> Specifically, it seems like find_last_bit used
Two more comments on the code. Two minor, but one that
seems like a bug, so for now, it's
Nacked-by: George Spelvin
Specifically, it seems like find_last_bit used to ignore trailing
garbage in the bitmap, but now will stop searching if the last word
contains some set bits not within size.
Th
This basically has my Reviewed-by: (I'll send it in a few hours
when I have time to do a real final copy-editing), but a few minor
notes:
>+ /*
>+ * This is an equvalent for:
>+ *
>+ * tmp = find_set ? addr[start / BITS_PER_LONG]
>+
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