somebody could explain this?

Hello, I'm using PostgreSQL 8.0.4 in Fedora Core 3, right now I'm learning a
little about the postgresql internals and the way some kind of SPs could be
written in c language; I found something really weird and I cannot explain
to me this behavior:

#include "postgres.h"
#include "fmgr.h"

PG_FUNCTION_INFO_V1(test);

Datum
repeat_item(PG_FUNCTION_ARGS)
{
int num_times;

num_times = PG_GETARG_FLOAT8(0) * 100;
PG_RETURN_INT32(num_times);
}

Inside psql this happens:

# Create or replace function test(float) returns integer as 'test.so'
language 'c' stable;

select test(0.1);
Returns 10

Select test(0.11);
Returns 11

Select test(0.12)
Returns 11

Select test(0.13)
Returns 13

Select test(0.14)
Returns 14

Select test(0.15)
Returns 14

What Is happening here?