Arm® A64 Instruction Set Architecture: Future Architecture Technologies in the A architecture profile | CSNEG: Conditional Select Negation.

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CSNEG

Conditional Select Negation returns, in the destination register, the value of the first source register if the condition is TRUE, and otherwise returns the negated value of the second source register.

This instruction is used by the alias CNEG.

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
sf	1	0	1	1	0	1	0	1	0	0	Rm					cond				0	1	Rn					Rd
	op																				o2

32-bit (sf == 0)

CSNEG <Wd>, <Wn>, <Wm>, <cond>

64-bit (sf == 1)

CSNEG <Xd>, <Xn>, <Xm>, <cond>

integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer datasize = if sf == '1' then 64 else 32;

Assembler Symbols

<Wd>	Is the 32-bit name of the general-purpose destination register, encoded in the "Rd" field.

<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.

<Xd>	Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.

<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.

<cond>

Is one of the standard conditions, encoded in the "cond" field in the standard way.

Alias Conditions

Alias	Is preferred when
CNEG	cond != '111x' && Rn == Rm

Operation

bits(datasize) result;
bits(datasize) operand1 = X[n];
bits(datasize) operand2 = X[m];

if ConditionHolds(cond) then
    result = operand1;
else
    result = NOT(operand2);
    result = result + 1;

X[d] = result;

Operational information

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.

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