crc32cb

CRC32C Byte

CRC32CB <Wd>, <Wn>, <Wm>

Updates CRC32C (Castagnoli) checksum with a byte.

Pseudocode Operation

Wd ← CRC32CPolynomial(Wn, Wm<7:0>)

Example

CRC32CB w0, w1, w2

Encoding

Binary Layout

11010110

28:21

20:16

010

15:13

11:10

9:5

4:0

Format Data Processing

Opcode 0x1AC05000

Extension CRC

Operands

Wd
Destination 32-bit integer register
Wn
Acc
Wm
Data

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0x1AC05000	CRC32CB <Wd>, <Wn>, <Wm>		A64		0 \| 0 \| 0 \| 11010110 \| Rm \| 010 \| 1 \| 00 \| Rn \| Rd

Description

CRC32C checksum 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.

Operation

bits(32) acc = X[n, 32];    // accumulator
bits(size) val = X[m, size];    // input value
bits(32) poly = 0x1EDC6F41<31:0>;

bits(32+size) tempacc = BitReverse(acc):Zeros(size);
bits(size+32) tempval = BitReverse(val):Zeros(32);

// Poly32Mod2 on a bitstring does a polynomial Modulus over {0,1} operation
X[d, 32] = BitReverse(Poly32Mod2(tempacc EOR tempval, poly));