A UDF that is used for the algorithmic decompression of previously compressed character columns must call FNC_GetOutputBufferSize to determine the maximum length of the string to build for the return argument. This is necessary because the UDF can declare a BYTE(n), VARBYTE(n), CHAR(n), or VARCHAR(n) return argument where the value of n is greater than or equal to the size of n for the column data type.
This function can only be called from within a scalar or aggregate UDF.