CCMP (register)

Conditional compare (register)

This instruction sets the value of the condition flags to the result of the comparison of two registers 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
	1	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)

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

64-bit (sf == 1)

CCMP <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, NOT(operand2), '1');
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.