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CSEL

If the condition is true, Conditional Select writes the value of the first source register to the destination register. If the condition is false, it writes the value of the second source register to the destination register.

313029282726252423222120191817161514131211109876543210
sf0011010100Rmcond00RnRd
opo2

32-bit (sf == 0)

CSEL <Wd>, <Wn>, <Wm>, <cond>

64-bit (sf == 1)

CSEL <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.

Operation

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

if ConditionHolds(cond) then
    result = operand1;
else
    result = operand2;

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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