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CLZ

Count Leading Zeros counts the number of binary zero bits before the first binary one bit in the value of the source register, and writes the result to the destination register.

313029282726252423222120191817161514131211109876543210
sf101101011000000000100RnRd
op

32-bit (sf == 0)

CLZ <Wd>, <Wn>

64-bit (sf == 1)

CLZ <Xd>, <Xn>

integer d = UInt(Rd);
integer n = UInt(Rn);
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 general-purpose source register, encoded in the "Rn" 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 general-purpose source register, encoded in the "Rn" field.

Operation

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

result = CountLeadingZeroBits(operand1);
X[d] = result<datasize-1:0>;

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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