crc32b

CRC32 Byte

CRC32B <Wd>, <Wn>, <Wm>

Updates CRC32 checksum with a byte.

Pseudocode Operation

Wd ← CRC32Polynomial(Wn, Wm<7:0>)

Example

CRC32B w0, w1, w2

Encoding

Binary Layout
0
31
0
30
0
29
11010110
28:21
Rm
20:16
010
15:13
0
12
00
11:10
Rn
9:5
Rd
4:0
 
Format Data Processing
Opcode 0x1AC04000
Extension CRC

Operands

  • Wd
    Destination 32-bit integer register
  • Wn
    Accumulator
  • Wm
    Data

Related

Other forms of crc32b

More in CRC

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding Instruction ISA Bit pattern
0x1AC04000 CRC32B <Wd>, <Wn>, <Wm> A64 0 | 0 | 0 | 11010110 | Rm | 010 | 0 | 00 | Rn | Rd

Description

CRC32 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 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.

Operation

bits(32) acc = X[n, 32];    // accumulator
bits(size) val = X[m, size];    // input value
bits(32) poly = 0x04C11DB7<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));