Does ctz access memory?
No. It reads integer register operands and writes rd only.
CTZ
RISC-V CTZ Instruction Details
Instruction ManualI-type (OP-IMM)Count trailing zero bits
Instruction Syntax
ctz rd, rs1
Operand Breakdown
This is a I-type (OP-IMM)-format instruction. Confirm operand positions based on the assembly syntax.
ZbbBit ManipulationInteger Operation
Related Search Terms
Instruction Behavior
ctz returns the number of consecutive zero bits starting at the least-significant bit of rs1.
CTZ Decode And Execute Animation
Starts with machine-code field decoding, then shows operand reads, instruction-specific execution, and ISA-visible state update.
rd
rs1
ctz
,
Execution Context
t1(x6)
0x00000014
31..20
19..15
14..12
11..7
6..0
011000000001
fixed imm[11:0]
00110
rs1
001
funct3
00101
rd
0010011
opcode
Execution Data Path
instruction
0x60131293
opcode
0010011 -> OP-IMM
funct3
001 -> CTZ
fixed imm[11:0]
011000000001 -> CTZ selector
rd / rs1
t0(x5) / t1(x6)=0x00000014
fixed imm[11:0]
011000000001 selects CTZ (not an arithmetic immediate)
zero-bit scan
scan rs1[0] toward rs1[31] for the first 1 -> 2
x5
t0(x5) = 0x00000002
Current Step
Concept Step: receive the 32-bit instruction encoding
The machine code is split by the current instruction format; the animation starts from encoding/decode.
encoding: 0x60131293
syntax : ctz t0(x5), t1(x6)
result : t0(x5) = 0x00000002
Architectural Result
t0(x5) = 0x00000002
This animation shows ISA-visible decode and state changes, not any specific CPU pipeline, cache, prediction, or timing implementation.
Quick Understanding & Search Notes
ctz returns the number of consecutive zero bits starting at the least-significant bit of rs1.
CTZ is an OP-IMM instruction in the Zbb basic bit-manipulation extension and operates on an XLEN-wide integer register value.
If the input is zero, the result is XLEN.
Common Usage Scenarios
Bit Operations & Masks
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 I-type (OP-IMM).
- 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.