BIT

Bitwise insert if true

This instruction inserts each bit from the first source SIMD&FP register into the SIMD&FP destination register if the corresponding bit of the second source SIMD&FP register is 1, otherwise leaves the bit in the destination register unchanged.

Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

Encoding: Three registers of the same type

Variants: FEAT_AdvSIMD (ARMv8.0)

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
0		1	0	1	1	1	0	1	0	1						0	0	0	1	1	1
	Q	U						opc2			Rm					opcode						Rn					Rd

BIT <Vd>.<T>, <Vn>.<T>, <Vm>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer datasize = 64 << UInt(Q);

Operation

CheckFPAdvSIMDEnabled64();

constant bits(datasize) operand1 = V[d, datasize];
constant bits(datasize) operand2 = V[m, datasize];
constant bits(datasize) operand3 = V[n, datasize];
V[d, datasize] = operand1 EOR ((operand1 EOR operand3) AND operand2);

Explanations

<Vd>: Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
<T>: <Vn>: Is the name of the first SIMD&FP source register, encoded in the "Rn" field.
<Vm>: Is the name of the second SIMD&FP source register, encoded in the "Rm" field.

Operational Notes

If PSTATE.DIT is 1:

• The execution time of this instruction is independent of:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.
• The response of this instruction to asynchronous exceptions does not vary based on:
  • The values of the data supplied in any of its registers.
  • The values of the NZCV flags.