Does FROUND.D write an integer register?
No. The result is written to floating-point register f[rd]; the floating-point value is integral.
FROUND.D
RISC-V FROUND.D Instruction Details
Instruction ManualR-typeRound a double-precision floating-point value to an integral value in the same FP format, without setting NX.
Instruction Syntax
fround.d rd, rs1, rm
Operand Breakdown
rd: destination floating-point register receiving the rounded result in the same format.
rs1: the only source floating-point register; the encoded rs2 field is fixed to 00100 (decimal 4), not a second source floating-point register.
rm: rounding-mode field; rm=111 uses the dynamic frm rounding mode.
ZfaDFP Precision
Instruction Behavior
FROUND.D rounds the double-precision FP value in f[rs1] to an integral value according to rm and writes it in D format to f[rd]. Zero and infinity are copied unchanged; a signaling NaN sets NV and no other exception flags. Unlike FROUNDNX, FROUND does not set NX.
FROUND.D Decode And Execute Animation
Shows the Zfa + D-extension double-precision OP-FP flow: decode fields, read FP operands, perform FROUND semantics, then write rd.
rd
rs1
rm
fround.d
,
,
Execution Context
FLEN=>=64 / fmt=D (01)
rounding: RNE nearest-even
fflags: FROUND example leaves fflags clear
31..27
26..25
24..20
19..15
14..12
11..7
6..0
01000
FROUND
01
fmt=D
00100
rs2=4 (roundToIntegral)
01011
rs1
000
rm
01010
rd
1010011
OP-FP
Execution Data Path
instruction
0x42458553
opcode
1010011 -> OP-FP
funct5/fmt
01000 + D(01) -> FROUND.D
rm
000 -> RNE nearest-even
rd/rs
fa0(f10) / fa1(f11) / rs2=00100 (fixed)
read
1.5
FP op
roundToIntegral(1.5, RNE nearest-even) = 2.0
write
fa0(f10) = 2.0; FROUND example leaves fflags clear
Current Step
Fetch: show the 32-bit OP-FP encoding
The word is split as an R-type OP-FP instruction; double-precision OP-FP instructions use opcode 1010011.
encoding: 0x42458553
syntax : fround.d fa0(f10), fa1(f11), rne
result : fa0(f10) = 2.0; FROUND example leaves fflags clear
This bounded teaching model computes whitelisted finite examples plus zero, infinity, and NaN; FROUND.D writes the integral value in D format. Zero and infinity are copied. FROUND does not set NX and sets no exception flags other than NV.
Double-precision Calculation
rs1
fa1(f11) = 1.5
rs2
ft4(f4) = 0.0
result
roundToIntegral(1.5, RNE nearest-even) = 2.0
This bounded teaching model computes whitelisted finite examples plus zero, infinity, and NaN; FROUND.D writes the integral value in D format. Zero and infinity are copied. FROUND does not set NX and sets no exception flags other than NV.
This animation shows only Zfa + D-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
FROUND.D differs from FCVT by output type: FROUND.D still writes a floating-point register, with the value rounded to an integral value. FROUND deliberately does not report inexact NX.
Its OP-FP encoding is funct5=01000, fmt=01 (D), rs2=00100, rs1, rm, rd, and opcode=1010011.
rm selects the rounding direction; rm=111 selects dynamic rounding from frm.
Zero and infinity are copied unchanged; a signaling NaN sets NV, while FROUND sets neither NX nor any other exception flag.
Common Usage Scenarios
Floating-Point Rounding
Understand this scenario with real code like «fround.d f10, f11, rup ; round f11 toward +∞».
Numeric Format Handling
Understand this scenario with real code like «fround.d f10, f11, rup ; round f11 toward +∞».
Pre-Use Checklist
Syntax Check
- rd: destination floating-point register receiving the rounded result in the same format.
- rs1: the only source floating-point register; the encoded rs2 field is fixed to 00100 (decimal 4), not a second source floating-point register.
- 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
FROUND does not set NX; use FROUNDNX when inexact reporting is needed.
The result is still floating-point, not an integer-register result; use FCVT for an integer result.
rm controls the direction for rounding to an integral value.
FAQ
How does FROUND.D differ from the other FROUND form?
FROUND does not set NX; FROUNDNX sets NX only when the input differs from the rounded result and is not NaN.