BUG #3629: Memory Allocation Error

The following bug has been logged online:

Bug reference: 3629
Logged by: zhuge
Email address: zhuge(at)Rinaix(dot)cn
PostgreSQL version: 8.1.9
Operating system: Linux
Description: Memory Allocation Error
Details:

I wrote and compiled and linked a C function, add_float, which returns float
in C like following:

PG_FUNCTION_INFO_V1(add_float);

Datum
add_float(PG_FUNCTION_ARGS)
{
float arg = PG_GETARG_FLOAT8(0);

PG_RETURN_FLOAT8(arg + 10);
}

After having loaded it into database, executed the SQL command, "select
ad_float(2.90)", but one error occured. The error message is "Error: invalid
memory alloc request size 4294967290" .

However I changed the above function as following:

Datum
add_integer(PG_FUNCTION_ARGS)
{
int32 arg = PG_GETARG_INT32(0);

PG_RETURN_INT32(arg + 10);
}

and executed the SQL command, "select add_integer(5)", and the result is:
add_integer
----------
15

In another word, the function can NOT return float BUT return integer. Why?
Please help me.

Thank you very much.