Does clz access memory?
No. It reads integer register operands and writes rd only.
CLZ
RISC-V CLZ Instruction Details
Instruction ManualI-type (OP-IMM)Count leading zero bits
Instruction Syntax
clz 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
clz returns the number of consecutive zero bits starting at the most-significant bit of rs1.
CLZ Decode And Execute Animation
Starts with machine-code field decoding, then shows operand reads, instruction-specific execution, and ISA-visible state update.
rd
rs1
clz
,
Execution Context
t1(x6)
0x00000014
31..20
19..15
14..12
11..7
6..0
011000000000
fixed imm[11:0]
00110
rs1
001
funct3
00101
rd
0010011
opcode
Execution Data Path
instruction
0x60031293
opcode
0010011 -> OP-IMM
funct3
001 -> CLZ
fixed imm[11:0]
011000000000 -> CLZ selector
rd / rs1
t0(x5) / t1(x6)=0x00000014
fixed imm[11:0]
011000000000 selects CLZ (not an arithmetic immediate)
zero-bit scan
scan rs1[31] toward rs1[0] for the first 1 -> 27
x5
t0(x5) = 0x0000001B
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: 0x60031293
syntax : clz t0(x5), t1(x6)
result : t0(x5) = 0x0000001B
Architectural Result
t0(x5) = 0x0000001B
This animation shows ISA-visible decode and state changes, not any specific CPU pipeline, cache, prediction, or timing implementation.
Quick Understanding & Search Notes
clz returns the number of consecutive zero bits starting at the most-significant bit of rs1.
CLZ 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 «clz x10, x11 ; x10 = number of leading 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 clz interpret signed numbers?
These bit operations work on bit patterns directly; aside from the specified word-width selection, arithmetic signed magnitude is not used.