CCMN (register)

Conditional compare negative (register)

This instruction sets the value of the condition flags to the result of the comparison of a register value and the inverse of another register value if the condition is TRUE, and an immediate value otherwise.

Encoding: Integer

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	1	1	0	1	0	0	1	0										0	0						0
sf	op	S									Rm					cond					o2	Rn					o3	nzcv

32-bit (sf == 0)

CCMN <Wn>, <Wm>, #<nzcv>, <cond>

64-bit (sf == 1)

CCMN <Xn>, <Xm>, #<nzcv>, <cond>

Decoding algorithm

constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer datasize = 32 << UInt(sf);
constant bits(4) condition = cond;
bits(4) flags = nzcv;

Operation

if ConditionHolds(condition) then
    constant bits(datasize) operand1 = X[n, datasize];
    constant bits(datasize) operand2 = X[m, datasize];
    (-, flags) = AddWithCarry(operand1, operand2, '0');
PSTATE. = flags;

Explanations

<Wn>: Is the 32-bit name of the first general-purpose source register, encoded in the "Rn" field.
<Wm>: Is the 32-bit name of the second general-purpose source register, encoded in the "Rm" field.
<nzcv>: Is the flag bit specifier, an immediate in the range 0 to 15, giving the alternative state for the 4-bit NZCV condition flags, encoded in the "nzcv" field.
<cond>: <Xn>: Is the 64-bit name of the first general-purpose source register, encoded in the "Rn" field.
<Xm>: Is the 64-bit name of the second general-purpose 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.