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From: "Tomas Pilar (tpilar)" <tpilar@solarflare.com>
To: "Gao, Liming" <liming.gao@intel.com>,
	"edk2-devel@lists.01.org" <edk2-devel@lists.01.org>
Subject: Re: [PATCH] MdePkg/BaseLib: Add bit field Hamming weight calculation methods
Date: Mon, 2 Jul 2018 10:31:00 +0100	[thread overview]
Message-ID: <fe11261a-c714-58a3-abcd-7ef1ed33a27b@solarflare.com> (raw)
In-Reply-To: <4A89E2EF3DFEDB4C8BFDE51014F606A14E2A0C7F@SHSMSX104.ccr.corp.intel.com>

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 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
>>
>> _______________________________________________
>> edk2-devel mailing list
>> edk2-devel@lists.01.org
>> https://lists.01.org/mailman/listinfo/edk2-devel



  reply	other threads:[~2018-07-02  9:31 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-29  9:41 [PATCH] MdePkg/BaseLib: Add bit field Hamming weight calculation methods Tomas Pilar (tpilar)
2018-07-02  8:22 ` Gao, Liming
2018-07-02  9:31   ` Tomas Pilar (tpilar) [this message]
2018-07-02  9:32     ` Tomas Pilar (tpilar)
2018-07-02 18:57 ` Evan Lloyd
2018-07-03  9:47   ` Tomas Pilar (tpilar)
2018-07-03 13:25     ` Gao, Liming

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