Does ctz access memory?
No. It reads integer register operands and writes rd only.
CTZ
RISC-V CTZ Instruction Details
Instruction ManualR-typeCount trailing zero bits
Instruction Syntax
ctz rd, rs1
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
BZbbBit ManipulationInteger Operation
Related Search Terms
Instruction Encoding
31..20
imm[11:0]
19..15
rs1
14..12
funct3
11..7
rd
6..0
opcode
CTZ uses opcode 0010011 (0x13), funct3 001, funct7 0110000. The rs1 field selects the source register, the 12-bit immediate provides the second operand, and rd selects the destination.
Format: I-type
opcode: 0010011 (0x13)
funct3: 001 (0x1)
funct7: 0110000 (0x30)
Instruction Behavior
ctz returns the number of consecutive zero bits starting at the least-significant bit of rs1.
Quick Understanding & Search Notes
ctz returns the number of consecutive zero bits starting at the least-significant bit of rs1.
These instructions are part of a B-extension subset and operate on XLEN-wide integer register values.
If the input is zero, the result is XLEN.
Common Usage Scenarios
Address & Pointer
Understand this scenario with real code like «ctz x10, x11 ; x10 = number of trailing zeros in x11».
Bit Operations & Masks
Understand this scenario with real code like «ctz x10, x11 ; x10 = number of trailing zeros in x11».
Cache & Hints
Understand this scenario with real code like «ctz x10, x11 ; x10 = number of trailing zeros in x11».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is R-type.
- Confirm the operand order matches the example.
Semantic Check
- Ensure the destination register usage is compatible with the calling convention.
- Confirm this is not the lower-level form of a pseudo-instruction expansion.
Pitfalls / Common Confusions
If the input is zero, the result is XLEN.
FAQ
Does ctz interpret signed numbers?
These bit operations work on bit patterns directly; aside from the specified word-width selection, arithmetic signed magnitude is not used.