6.6.3.2.1 Subnormal Number Handling

Should any floating-point calculation generate a subnormal result, the FSR.UDF will be set; if it is not already set, the sticky status FSR.UDFS will also be set. In addition, if any instruction is presented with a subnormal operand value, FSR.SUBO will be set. If it is not already set, the sticky status FSR.SUBOS will also be set.