Why does FSQRT.H have no rs2 operand?
FSQRT is a unary FP operation. The machine encoding still has an rs2 field, but it is fixed to 00000; the page animation shows it as an encoded field rather than a syntax input.
FSQRT.H
RISC-V FSQRT.H Instruction Details
Instruction ManualR-typeHalf-precision floating-point square root: rd = sqrt(rs1).
Instruction Syntax
fsqrt.h rd, rs1, rm
Operand Breakdown
rd: destination floating-point register receiving the square-root result.
rs1: the only source floating-point register; the encoded rs2 field is fixed to 00000 and is not a syntax operand.
rm: rounding-mode field; rm=111 uses the dynamic frm rounding mode.
ZfhFloating-Point Arithmetic
Instruction Behavior
FSQRT.H computes the half-precision floating-point square root, rounds according to rm or the dynamic rounding mode, and writes rd. A negative nonzero finite operand or -infinity produces canonical NaN and sets NV; sqrt(-0) remains -0.
FSQRT.H Decode And Execute Animation
Shows the Zfh-extension half-precision OP-FP flow: decode fields, read FP operands, perform FSQRT semantics, then write rd.
rd
rs1
rm
fsqrt.h
,
,
Execution Context
FLEN=>=32 / fmt=H (10)
rounding: RNE nearest-even
fflags: example fflags remains 0
31..27
26..25
24..20
19..15
14..12
11..7
6..0
01011
FSQRT
10
fmt=H
00000
rs2
01011
rs1
000
rm
01010
rd
1010011
OP-FP
Execution Data Path
instruction
0x5C058553
opcode
1010011 -> OP-FP
funct5/fmt
01011 + H(10) -> FSQRT.H
rm
000 -> RNE nearest-even
rd/rs
fa0(f10) / fa1(f11) / rs2=00000
read
2.25
FP op
sqrt(2.25) = 1.5
write
fa0(f10) = 1.5; example fflags remains 0
Current Step
Fetch: show the 32-bit OP-FP encoding
The word is split as an R-type OP-FP instruction; half-precision OP-FP instructions use opcode 1010011.
encoding: 0x5C058553
syntax : fsqrt.h fa0(f10), fa1(f11), rne
result : fa0(f10) = 1.5; example fflags remains 0
The default example sqrt(9.0)=3.0 is exactly representable, so example fflags remains 0.
Half-precision Calculation
rs1
fa1(f11) = 2.25
result
sqrt(2.25) = 1.5
The default example sqrt(9.0)=3.0 is exactly representable, so example fflags remains 0.
This animation shows only Zfh-extension ISA-visible OP-FP encoding, example numeric results, and fflags relationship; it does not model FPU pipelines, latency, every IEEE 754 corner case, or microarchitecture.
Quick Understanding & Search Notes
FSQRT.H is Zfh half-precision floating-point square root. It uses OP-FP encoding with funct5=01011, fmt=H(10), and rs2 fixed to 00000; it reads only the rs1 half-precision value, rounds according to rm or dynamic frm, and writes rd.
FSQRT.H has rs2 as a fixed encoded field, not an assembly operand; the syntax contains only rd, rs1, and rm.
Negative nonzero finite inputs and -infinity take the invalid-operation path; sqrt(-0) remains -0.
The animation defaults to exact examples such as sqrt(9.0)=3.0; NaNs, infinities, negative inputs, and inexact rounding are covered by static text.
Common Usage Scenarios
Floating Point Basic
Understand this scenario with real code like «fsqrt.h f10, f11, rne ; f10 = sqrt(f11)».
Numerical Computing
Understand this scenario with real code like «fsqrt.h f10, f11, rne ; f10 = sqrt(f11)».
Pre-Use Checklist
Syntax Check
- rd: destination floating-point register receiving the square-root result.
- rs1: the only source floating-point register; the encoded rs2 field is fixed to 00000 and is not a syntax operand.
- rm: rounding-mode field; rm=111 uses the dynamic frm rounding mode.
Semantic Check
- Confirm the floating-point format suffix (.H/.S/.D/.Q) matches the data width.
- Decide whether software must inspect fflags for NV, DZ, OF, UF, or NX.
Pitfalls / Common Confusions
Rounding comes from the rm field; rm=111 uses the dynamic frm rounding mode.
Floating-point exceptions are recorded in fflags, not as integer branch conditions or integer traps.
The square-root negative-input edge case distinguishes -0 from other negative values.
FAQ
How does FSQRT.H handle negative inputs?
Negative nonzero finite numbers and -infinity raise the invalid-operation flag and produce a NaN result; -0 is a special zero value and sqrt(-0) remains -0.