Max column number.

Hi,

I'm using postgresql 9 and I'd like to know if there is a way to "ask" if
when I'm going to add a column, I'm exceeding the max number of columns.
I've found that the max number of columns is 1600 and It's depends of the
data types.
I've made a test adding 1600 columns using different data types and I didn't
have any problem. The problem was when I tried to insert data.

ERROR: row is too big: size 8168, maximum size 8160

I know that the row limit size is 8k by default, but I need a way to prevent
this exception.

For example, my table have 600 columns and I insert a row with values for
each column and the row size is 8000. So, in this case If I want to prevent
errors, I can't add more columns, but to do that I need to know about this
limit situation.
Something like:
"If I'm not going to exceed the size limit, then I can add a new column"

Thanks in advance,
Miguel.