Re: [PATCH] MdePkg/BaseLib: Add bit field Hamming weight calculation methods

["Tomas Pilar (tpilar)" <tpilar@solarflare.com>]

On 02/07/18 10:31, Tomas Pilar (tpilar) wrote:
> Hi Liming,
>
> Using a bitmask to advertise capabilities is a common mechanism in driver APIs (e.g. network link capabilites). In some cases, one needs to allocate a buffer per capability 
Apologies, I meant 'buffer with size proportional to advertised capabilites'.
> and thus they need to count the set bits. The algorithms to do that are fairly well known and generally provided in bitfield libraries. I expect that this will be useful to quite a number of IHV developers (as well as me).
>
> Cheers,
> Tom
>
> On 02/07/18 09:22, Gao, Liming wrote:
>> Tomas:
>>   Could you share some background what code depends on new added APIs? 
>>
>> Thanks
>> Liming
>>> -----Original Message-----
>>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
>>> Tomas Pilar (tpilar)
>>> Sent: Friday, June 29, 2018 5:42 PM
>>> To: edk2-devel@lists.01.org
>>> Subject: [edk2] [PATCH] MdePkg/BaseLib: Add bit field Hamming weight
>>> calculation methods
>>>
>>> Add 32-bit and 64-bit functions that count number of set bits in a bitfield
>>> using the divide-and-count method.
>>>
>>> Contributed-under: TianoCore Contribution Agreement 1.1
>>> Signed-off-by: Tomas Pilar <tpilar@solarflare.com>
>>> ---
>>> MdePkg/Include/Library/BaseLib.h  | 56 +++++++++++++++++++++++++++
>>> MdePkg/Library/BaseLib/BitField.c | 79
>>> +++++++++++++++++++++++++++++++++++++++
>>> 2 files changed, 135 insertions(+)
>>>
>>> diff --git a/MdePkg/Include/Library/BaseLib.h
>>> b/MdePkg/Include/Library/BaseLib.h
>>> index 1db3a04..7eb0488 100644
>>> --- a/MdePkg/Include/Library/BaseLib.h
>>> +++ b/MdePkg/Include/Library/BaseLib.h
>>> @@ -4609,6 +4609,62 @@ BitFieldAndThenOr64 (
>>>   IN      UINT64                    OrData
>>>   );
>>>
>>> +/**
>>> +  Reads a bit field from a 32-bit value, counts and returns
>>> +  the number of set bits.
>>> +
>>> +  Counts the number of set bits in the  bit field specified by
>>> +  StartBit and EndBit in Operand. The count is returned.
>>> +
>>> +  If StartBit is greater than 31, then ASSERT().
>>> +  If EndBit is greater than 31, then ASSERT().
>>> +  If EndBit is less than StartBit, then ASSERT().
>>> +
>>> +  @param  Operand   Operand on which to perform the bitfield operation.
>>> +  @param  StartBit  The ordinal of the least significant bit in the bit field.
>>> +                    Range 0..31.
>>> +  @param  EndBit    The ordinal of the most significant bit in the bit field.
>>> +                    Range 0..31.
>>> +
>>> +  @return The number of bits set between StartBit and EndBit.
>>> +
>>> +**/
>>> +UINT8
>>> +EFIAPI
>>> +BitFieldHammingWeight32 (
>>> +  IN       UINT32                   Operand,
>>> +  IN       UINTN                    StartBit,
>>> +  IN       UINTN                    EndBit
>>> +  );
>>> +
>>> +/**
>>> +   Reads a bit field from a 64-bit value, counts and returns
>>> +   the number of set bits.
>>> +
>>> +   Counts the number of set bits in the  bit field specified by
>>> +   StartBit and EndBit in Operand. The count is returned.
>>> +
>>> +   If StartBit is greater than 63, then ASSERT().
>>> +   If EndBit is greater than 63, then ASSERT().
>>> +   If EndBit is less than StartBit, then ASSERT().
>>> +
>>> +   @param  Operand   Operand on which to perform the bitfield operation.
>>> +   @param  StartBit  The ordinal of the least significant bit in the bit field.
>>> +   Range 0..63.
>>> +   @param  EndBit    The ordinal of the most significant bit in the bit field.
>>> +   Range 0..63.
>>> +
>>> +   @return The number of bits set between StartBit and EndBit.
>>> +
>>> +**/
>>> +UINT8
>>> +EFIAPI
>>> +BitFieldHammingWeight64 (
>>> +  IN       UINT64                   Operand,
>>> +  IN       UINTN                    StartBit,
>>> +  IN       UINTN                    EndBit
>>> +  );
>>> +
>>> //
>>> // Base Library Checksum Functions
>>> //
>>> diff --git a/MdePkg/Library/BaseLib/BitField.c
>>> b/MdePkg/Library/BaseLib/BitField.c
>>> index d2d3150..af06db8 100644
>>> --- a/MdePkg/Library/BaseLib/BitField.c
>>> +++ b/MdePkg/Library/BaseLib/BitField.c
>>> @@ -920,3 +920,82 @@ BitFieldAndThenOr64 (
>>>            OrData
>>>            );
>>> }
>>> +
>>> +/**
>>> +  Reads a bit field from a 32-bit value, counts and returns
>>> +  the number of set bits.
>>> +
>>> +  Counts the number of set bits in the  bit field specified by
>>> +  StartBit and EndBit in Operand. The count is returned.
>>> +
>>> +  If StartBit is greater than 31, then ASSERT().
>>> +  If EndBit is greater than 31, then ASSERT().
>>> +  If EndBit is less than StartBit, then ASSERT().
>>> +
>>> +  @param  Operand   Operand on which to perform the bitfield operation.
>>> +  @param  StartBit  The ordinal of the least significant bit in the bit field.
>>> +                    Range 0..31.
>>> +  @param  EndBit    The ordinal of the most significant bit in the bit field.
>>> +                    Range 0..31.
>>> +
>>> +  @return The number of bits set between StartBit and EndBit.
>>> +
>>> +**/
>>> +UINT8
>>> +EFIAPI
>>> +BitFieldHammingWeight32 (
>>> +  IN       UINT32                   Operand,
>>> +  IN       UINTN                    StartBit,
>>> +  IN       UINTN                    EndBit
>>> +  )
>>> +{
>>> +  ASSERT (EndBit < 32);
>>> +  ASSERT (StartBit <= EndBit);
>>> +
>>> +  UINT32 Count = BitFieldRead32 (Operand, StartBit, EndBit);
>>> +  Count -= ((Count >> 1) & 0x55555555);
>>> +  Count = (Count & 0x33333333) + ((Count >> 2) & 0x33333333);
>>> +  Count += Count >> 4;
>>> +  Count &= 0x0F0F0F0F;
>>> +  Count += Count >> 8;
>>> +  Count += Count >> 16;
>>> +
>>> +  return (UINT8) Count & 0x3F;
>>> +}
>>> +
>>> +/**
>>> +   Reads a bit field from a 64-bit value, counts and returns
>>> +   the number of set bits.
>>> +
>>> +   Counts the number of set bits in the  bit field specified by
>>> +   StartBit and EndBit in Operand. The count is returned.
>>> +
>>> +   If StartBit is greater than 63, then ASSERT().
>>> +   If EndBit is greater than 63, then ASSERT().
>>> +   If EndBit is less than StartBit, then ASSERT().
>>> +
>>> +   @param  Operand   Operand on which to perform the bitfield operation.
>>> +   @param  StartBit  The ordinal of the least significant bit in the bit field.
>>> +   Range 0..63.
>>> +   @param  EndBit    The ordinal of the most significant bit in the bit field.
>>> +   Range 0..63.
>>> +
>>> +   @return The number of bits set between StartBit and EndBit.
>>> +
>>> +**/
>>> +UINT8
>>> +EFIAPI
>>> +BitFieldHammingWeight64 (
>>> +  IN       UINT64                   Operand,
>>> +  IN       UINTN                    StartBit,
>>> +  IN       UINTN                    EndBit
>>> +  )
>>> +{
>>> +  ASSERT (EndBit < 64);
>>> +  ASSERT (StartBit <= EndBit);
>>> +
>>> +  UINT64 BitField = BitFieldRead64 (Operand, StartBit, EndBit);
>>> +  UINT8 Count = BitFieldHammingWeight32 (BitField, 0, 31);
>>> +  return Count + BitFieldHammingWeight32(RShiftU64(BitField, 32), 0, 31);
>>> +}
>>> +
>>> --
>>> 2.9.5
>>>
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