Re: [HACKERS] Binary cursor header changed from 20 to 16 Bytes?

Bruce Momjian wrote:

>
> > No, it works just fine. All you have to do is to swap the endian format (Linux Intel
> > is little endian; SGI is big endian). We've been using this approach since Postgres
> > 6.3.
> >
>
> What doesn't work?  Floats?  Alignment problems?
>

The only thing that seems to have problems is when you select multiple variables. For
this case, you have to put all of your arrays at the end.

e.g.      sprintf(data_string, "DECLARE data_cursor BINARY CURSOR "         "FOR SELECT repetition, cycle,
time_instantsFROM %s_proc WHERE "          "subject= '%s' and arm = '%s' and rep = %s and cycle = %s",
task_name,subject_name[subject], arm_name[arm],         repetition_name[i], cycle_name[j]);
 
        res = PQexec(conn, data_string);        if (PQresultStatus(res) != PGRES_COMMAND_OK) {
printf("\n\nERRORissuing command ... %s\n", data_string);             exit_nicely(conn);        }        PQclear(res);
     sprintf(data_string, "FETCH ALL IN data_cursor");        res = PQexec(conn, data_string);        if
(PQresultStatus(res)!= PGRES_TUPLES_OK) {             printf("\n\nERROR issuing command ... %s\n", data_string);
    exit_nicely(conn);         }
 
        /* Move binary-transferred data to desired variable float array */        memmove(bin_time, (PQgetvalue(res, 0,
2)),(number_of_bins + 1) *
 
sizeof(float));
        PQclear(res);        switch_endians_4bytes(bin_time, number_of_bins + 1);        res = PQexec(conn, "CLOSE
data_cursor");       PQclear(res);        res = PQexec(conn, "END");        PQclear(res);
 


So in the above case, I can get the repetition (single int value), cycle (single int
value), and time_instants (variable array of float values) out as a binary cursor. But
need to put the variable array at the end to make it work correctly. In this case, I
don't need to offset by 16 bytes to get the 2nd and 3rd column (cycles and
time_instants); I only need to do this for the 1st column (repetition).

My switch_endians_4_bytes looks like this:

void switch_endians_4bytes(int *temp_array, int size_of_array)
{   short int test_endianess_word = 0x0001;   char *test_endianess_byte = (char *) &test_endianess_word;
   int i;   int temp_int;   char *temp_char, byte0, byte1, byte2, byte3;
   if (test_endianess_byte[0] == BIG_ENDIAN) {
        for (i = 0; i < size_of_array; i++) {
            temp_int = temp_array[i];            temp_char = (char *) (&temp_int);            byte0 = *temp_char;
    byte1 = *(++temp_char);            byte2 = *(++temp_char);            byte3 = *(++temp_char);            temp_char
=(char *) (&temp_int);            *temp_char = byte3;            *(++temp_char) = byte2;            *(++temp_char) =
byte1;           *(++temp_char) = byte0;            temp_array[i] = temp_int;        }   }
 
}


where BIG_ENDIAN is defined as 0. Because I test the machine at run-time for its
endianess, I can run this on both of my platforms and it will either switch or not switch
depending on the need (assuming that the server is on a little endian machine).

-Tony