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CRC32

CRC32 performs a cyclic redundancy check (CRC) calculation on a value held in a general-purpose register. It takes an input CRC value in the first source operand, performs a CRC on the input value in the second source operand, and returns the output CRC value. The second source operand can be 8, 16, or 32 bits. To align with common usage, the bit order of the values is reversed as part of the operation, and the polynomial 0x04C11DB7 is used for the CRC calculation.

In an Armv8.0 implementation, this is an OPTIONAL instruction. From Armv8.1, it is mandatory for all implementations to implement this instruction.

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .

A1
(FEAT_CRC32)

Decode for all variants of this encoding

if !IsFeatureImplemented(FEAT_CRC32) then Undefined(); end; let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let size : integer{} = 8 << UInt(sz); let crc32c : boolean = (C == '1'); if d == 15 || n == 15 || m == 15 then UnpredictableProcedure(); end; if size == 64 then UnpredictableProcedure(); end; if cond != '1110' then UnpredictableProcedure(); end;

CONSTRAINED UNPREDICTABLE behavior

If size == 64, then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The instruction executes with the additional decode: size = 32;.

If cond != '1110', then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The instruction executes unconditionally.
• The instruction executes conditionally.

T1
(FEAT_CRC32)

Decode for all variants of this encoding

if InITBlock() then UnpredictableProcedure(); end; if !IsFeatureImplemented(FEAT_CRC32) then Undefined(); end; let d : integer = UInt(Rd); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let size : integer{} = 8 << UInt(sz); let crc32c : boolean = (C == '1'); if d == 15 || n == 15 || m == 15 then UnpredictableProcedure(); end; if size == 64 then UnpredictableProcedure(); end;

CONSTRAINED UNPREDICTABLE behavior

If size == 64, then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The instruction executes with the additional decode: size = 32;.

Assembler Symbols