Re: [Qemu-devel] [PATCH v3 1/2] bitmap: get last word mask from nr directly

[Wei Yang]

On Mon, Aug 12, 2019 at 06:18:43PM +0200, Paolo Bonzini wrote:
>On 18/07/19 03:04, Wei Yang wrote:
>> The value left in nr is the number of bits for the last word, which
>> could be calculate the last word mask directly.
>> 
>> Remove the unnecessary size.
>
>Hi,
>
>the value left in nr is _not_ the number of bits for the last word if
>the start and the end are in the same word.  For example, if start %
>BITS_PER_LONG was 3 and nr == 1, you'd have:
>
>- before the patch BITMAP_LAST_WORD_MASK(4)
>
>- after the patch BITMAP_LAST_WORD_MASK(1)
>

You are right. I missed this case.

Thanks for pointing out.

>Paolo
>
>> Signed-off-by: Wei Yang <address@hidden>
>> 
>> ---
>> v2: refine bitmap_set_atomic too, suggested from Peter
>> ---
>>  util/bitmap.c | 9 +++------
>>  1 file changed, 3 insertions(+), 6 deletions(-)
>> 
>> diff --git a/util/bitmap.c b/util/bitmap.c
>> index 1753ff7f5b..5b15249796 100644
>> --- a/util/bitmap.c
>> +++ b/util/bitmap.c
>> @@ -160,7 +160,6 @@ int slow_bitmap_andnot(unsigned long *dst, const 
>> unsigned long *bitmap1,
>>  void bitmap_set(unsigned long *map, long start, long nr)
>>  {
>>      unsigned long *p = map + BIT_WORD(start);
>> -    const long size = start + nr;
>>      int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG);
>>      unsigned long mask_to_set = BITMAP_FIRST_WORD_MASK(start);
>>  
>> @@ -174,7 +173,7 @@ void bitmap_set(unsigned long *map, long start, long nr)
>>          p++;
>>      }
>>      if (nr) {
>> -        mask_to_set &= BITMAP_LAST_WORD_MASK(size);
>> +        mask_to_set &= BITMAP_LAST_WORD_MASK(nr);
>>          *p |= mask_to_set;
>>      }
>>  }
>> @@ -182,7 +181,6 @@ void bitmap_set(unsigned long *map, long start, long nr)
>>  void bitmap_set_atomic(unsigned long *map, long start, long nr)
>>  {
>>      unsigned long *p = map + BIT_WORD(start);
>> -    const long size = start + nr;
>>      int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG);
>>      unsigned long mask_to_set = BITMAP_FIRST_WORD_MASK(start);
>>  
>> @@ -208,7 +206,7 @@ void bitmap_set_atomic(unsigned long *map, long start, 
>> long nr)
>>  
>>      /* Last word */
>>      if (nr) {
>> -        mask_to_set &= BITMAP_LAST_WORD_MASK(size);
>> +        mask_to_set &= BITMAP_LAST_WORD_MASK(nr);
>>          atomic_or(p, mask_to_set);
>>      } else {
>>          /* If we avoided the full barrier in atomic_or(), issue a
>> @@ -221,7 +219,6 @@ void bitmap_set_atomic(unsigned long *map, long start, 
>> long nr)
>>  void bitmap_clear(unsigned long *map, long start, long nr)
>>  {
>>      unsigned long *p = map + BIT_WORD(start);
>> -    const long size = start + nr;
>>      int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG);
>>      unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start);
>>  
>> @@ -235,7 +232,7 @@ void bitmap_clear(unsigned long *map, long start, long 
>> nr)
>>          p++;
>>      }
>>      if (nr) {
>> -        mask_to_clear &= BITMAP_LAST_WORD_MASK(size);
>> +        mask_to_clear &= BITMAP_LAST_WORD_MASK(nr);
>>          *p &= ~mask_to_clear;
>>      }
>>  }
>> 
>

-- 
Wei Yang
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