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:[email protected]] On Behalf Of >> Tomas Pilar (tpilar) >> Sent: Friday, June 29, 2018 5:42 PM >> To: [email protected] >> 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 <[email protected]> >> --- >> 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 >> [email protected] >> https://lists.01.org/mailman/listinfo/edk2-devel _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
