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|
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))
```