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FLT.S

RISC-V FLT.S Instruction Details

Instruction ManualR-type

Single-precision floating-point less-than comparison; writes x[rd]=1 when true, otherwise 0.

Instruction Syntax

flt.s rd, rs1, rs2
Operand Breakdown
rd: destination integer register receiving a 0 or 1 comparison result.
rs1/rs2: source floating-point registers; compare instructions do not use an rm rounding mode.
FFloating-Point Compare
Related Search Terms
FLT.S instructionRISC-V FLT.Sflt.s syntaxflt.s NaNflt.s NV flagsingle-precision floating compare

Instruction Behavior

FLT.S compares the single-precision floating-point values in f[rs1] and f[rs2] and writes the Boolean result to integer register rd. It is a signaling comparison: any NaN, including a quiet NaN, sets NV and makes the result 0. The result is not a floating-point value and is not rounded by rm.

Quick Understanding & Search Notes

FLT.S writes the floating-point comparison result to integer register x[rd]. It has signaling-comparison semantics, so even a quiet NaN raises NV.

It writes 1 when rs1 < rs2 is true, otherwise 0; any NaN operand writes 0.
The instruction does not produce a floating-point result and has no rm rounding field.
RISC-V Unprivileged ISA Manual: F Extension

Common Usage Scenarios

Comparison & Detection

Understand this scenario with real code like «flt.s x10, f0, f1 # x10 = 1 if f0<f1 (signal NaN->NV,0)».

Floating-Point Conditions

Understand this scenario with real code like «flt.s x10, f0, f1 # x10 = 1 if f0<f1 (signal NaN->NV,0)».

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

Signaling comparisons set NV for any NaN; this differs from FEQ and Zfa quiet comparisons.
rd is an integer register and receives 0 or 1, not a floating-point value.
The comparison does not use the rm rounding mode.

FAQ

Is rd a floating-point register for FLT.S?

No. rd is an integer register holding the Boolean result 0 or 1.

What happens on NaN operands?

Any NaN operand makes the result 0 and sets NV.