Zfb also contains FROUND[.NX]

1 files changed, 37 insertions, 2 deletions

diff --git a/src/zfb.tex b/src/zfb.tex
index a765f8e..2d152ed 100644
--- a/src/zfb.tex
+++ b/src/zfb.tex
@@ -3,8 +3,8 @@ Instructions, Version 0.1}
 \label{chap:zfb}
 
 This chapter describes the Zfb standard extension, which adds instructions for
-quiet floating-point comparisons and for the IEEE 754-2019 minimum and maximum
-operations.
+quiet floating-point comparisons, IEEE 754-2019 minimum and maximum
+operations, and round-to-integer operations.
 For RV32D, the Zfb extension also adds instructions to transfer
 double-precision floating-point values to and from integer registers, and for
 RV64Q, it adds analogous instructions for quad-precision floating-point
@@ -34,6 +34,41 @@ These instructions implement the IEEE 754-2019 minimum and maximum operations.
 \end{commentary}
 
 
+\section{Round-to-Integer Instructions}
+
+The FROUND.S instruction rounds the single-precision floating-point number in
+floating-point register {\em rs1} to an integer, according to the rounding
+mode specified in the instruction's {\em rm} field.
+It then writes that integer, represented as a single-precision floating-point
+number, to floating-point register {\em rd}.
+Zero and infinite inputs are copied to {\em rd} unmodified.
+Signaling NaN inputs cause the invalid operation exception flag to be set; no
+other exception flags are set.
+FROUND.S is encoded like FCVT.S.D, but with {\em rs2}=4.
+
+The FROUND.NX.S instruction is defined similarly, but it also sets the inexact
+exception flag if the input differs from the rounded result and is not NaN.
+FROUND.NX.S is encoded like FCVT.S.D, but with {\em rs2}=5.
+
+If the D extension is implemented, FROUND.D and FROUND.NX.D instructions are
+analogously defined to operate on double-precision numbers.
+They are encoded like FCVT.D.S, but with {\em rs2}=4 and 5, respectively,
+
+If the Zfh extension is implemented, FROUND.H and FROUND.NX.H instructions are
+analogously defined to operate on half-precision numbers.
+They are encoded like FCVT.H.S, but with {\em rs2}=4 and 5, respectively,
+
+If the Q extension is implemented, FROUND.Q and FROUND.NX.Q instructions are
+analogously defined to operate on quad-precision numbers.
+They are encoded like FCVT.Q.S, but with {\em rs2}=4 and 5, respectively,
+
+\begin{commentary}
+The FROUND.NX.{\em fmt} instructions implement the IEEE 754-2019
+roundToIntegralExact operation, and the FROUND.{\em fmt} instructions
+implement the other operations in the roundToIntegral family.
+\end{commentary}
+
+
 \section{Comparison Instructions}
 
 The FLEQ.S and FLTQ.S instructions are defined like the FLE.S and FLT.S