From: lkcl <lkcl@web>
Date: Sun, 5 Jun 2022 01:37:40 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~1956
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=a6736456bde398a6f1efb587d24f2e470579d3bd;p=libreriscv.git

---

diff --git a/openpower/sv/fclass.mdwn b/openpower/sv/fclass.mdwn
index 1b4e29799..64c432e9f 100644
--- a/openpower/sv/fclass.mdwn
+++ b/openpower/sv/fclass.mdwn
@@ -4,9 +4,17 @@ In SV just as with [[sv/fcvt]] single precision is to be considered half-of-elwi
 
 based on xvtstdcsp v3.0B p768 the instruction performs analysis of the FP number to determine if it is Infinity, NaN, Denormalised or Zero and if so which sign.
 
-unlike xvtstdcsp the result is stored in a Condition Register specified by BF.
+unlike xvtstdcsp the result is stored in a Condition Register
+Field specified by BF.
 this allows it to be used as a predicate mask.  setb may be used to create the equivalent of xvtstdcsp if desired.
 
+The CR Field bits are set in a reasonably logical fashion:
+
+* BF.EQ is set if FRB is zero
+* BF.LE is set if FRB is non-normalises
+* BF.GE is set if FRB is infinite
+* BF.SO is set if FRB is NaN
+
 | 0.5| 6.8 |9..15 | 16.20 | 21...30 |31|  name   | Form    |
 | -- | --- | --   | ----- | ------- |--| ------- | ------  |
 | PO | BF  | DCMX | FRB   | XO      |dm2| fptstsp | X-Form|
@@ -23,10 +31,10 @@ class.Zero  <- (exponent = 0x00) & (fraction = 0)
 class.Denormal  <- (exponent = 0x00) & (fraction != 0)
 CR{BF} <- ((dcmx[0] & class.NaN & !sign)  |
            (dcmx[1] & class.NaN & sign))  ||
-          ((dcmx[6] & class.Denormal & !sign) |
-           (dcmx[7] & class.Denormal & sign)) ||
           ((dcmx[2] & class.Infinity & !sign) |
            (dcmx[3] & class.Infinity & sign)) ||
+          ((dcmx[6] & class.Denormal & !sign) |
+           (dcmx[7] & class.Denormal & sign)) ||
           ((dcmx[4] & class.Zero & !sign) |
            (dcmx[5] & class.Zero & sign))
 ```