SETF8, SETF16

Evaluation of 8-bit or 16-bit flag values

This instruction sets the PSTATE.NZV flags based on the value in the specified general-purpose register. SETF8 treats the value as an 8-bit value. SETF16 treats the value as a 16-bit value.

The PSTATE.C flag is not affected by these instructions.

Encoding: Integer

Variants: FEAT_FlagM (ARMv8.4)

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	0	1	1	1	0	1	0	0	0	0	0	0	0	0	0	0		0	0	1	0						0	1	1	0	1
sf	op	S									opcode2						sz					Rn					o3	mask

SETF8 (sz == 0)

SETF8 <Wn>

SETF16 (sz == 1)

SETF16 <Wn>

Decoding algorithm

if !IsFeatureImplemented(FEAT_FlagM) then EndOfDecode(Decode_UNDEF);
constant integer size = 8 << UInt(sz);
constant integer n = UInt(Rn);

Operation

constant bits(32) reg = X[n, 32];
PSTATE.N = reg;
PSTATE.Z = if (reg == Zeros(size)) then '1' else '0';
PSTATE.V = reg EOR reg;
//PSTATE.C unchanged;

Explanations

<Wn>: Is the 32-bit name of the general-purpose source register, encoded in the "Rn" 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.