CTZ

Count trailing zeros

This instruction counts the number of consecutive binary zero bits, starting from the least significant bit in the source register, and places the count in the destination register.

Integer class

(FEAT_CSSC)

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	1	0	0	0	0	0	0	0	0	0	1	1	0	Rn					Rd
		S									opcode2					opcode

32-bit encoding

(sf == 0)

CTZ <Wd>, <Wn>

64-bit encoding

(sf == 1)

CTZ <Xd>, <Xn>

Decode (all encodings)

if !IsFeatureImplemented(FEAT_CSSC) then EndOfDecode(Decode_UNDEF); constant integer datasize = 32 << UInt(sf); constant integer d = UInt(Rd); constant integer n = UInt(Rn);

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

constant bits(datasize) operand1 = X[n, datasize]; constant integer result = CountLeadingZeroBits(BitReverse(operand1)); X[d, datasize] = result<datasize-1:0>;

Operational information

This instruction is a data-independent-time instruction as described in About PSTATE.DIT.

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CTZ