CRC32C checksum
This instruction 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, 32, or 64 bits. To align with common usage, the bit order of the values is reversed as part of the operation, and the polynomial 0x1EDC6F41 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.
ID_AA64ISAR0_EL1.CRC32 indicates whether this instruction is supported.
| 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| sf | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | Rm | 0 | 1 | 0 | 1 | sz | Rn | Rd | |||||||||||||
| S | C | ||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_CRC32) then EndOfDecode(Decode_UNDEF); end; let d : integer{} = UInt(Rd); let n : integer{} = UInt(Rn); let m : integer{} = UInt(Rm); if sf == '1' && sz != '11' then EndOfDecode(Decode_UNDEF); end; if sf == '0' && sz == '11' then EndOfDecode(Decode_UNDEF); end; let size : integer{} = 8 << UInt(sz);
| <Wd> |
Is the 32-bit name of the general-purpose accumulator output register, encoded in the "Rd" field. |
| <Wn> |
Is the 32-bit name of the general-purpose accumulator input register, encoded in the "Rn" field. |
| <Wm> |
Is the 32-bit name of the general-purpose data source register, encoded in the "Rm" field. |
| <Xm> |
Is the 64-bit name of the general-purpose data source register, encoded in the "Rm" field. |
let acc : bits(32) = X{}(n); // accumulator let val : bits(size) = X{}(m); // input value let poly : bits(32) = 0x1EDC6F41[31:0]; let tempacc : bits(32+size) = BitReverse{32}(acc)::Zeros{size}; let tempval : bits(size+32) = BitReverse{size}(val)::Zeros{32}; // Poly32Mod2 on a bitstring does a polynomial Modulus over {0,1} operation X{32}(d) = BitReverse{32}(Poly32Mod2{32+size}(tempacc XOR tempval, poly));
This instruction is a data-independent-time instruction as described in About PSTATE.DIT.
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