Get double values from binary cursor

Hi, all.

i want to get a double values from binary cursor

in libpq < 7.4 it was simple
memcpy(&dfVal, PQgetvalue(...), sizeof(dfVal));

but now we have to convert data from MSB to LSB format
it is ok for int
but how to convert a double

i'am tried to write a simple program, but it does not work ....

#include <libpq-fe.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>

typedef unsigned int int4;
typedef double float8;

int main()
{
if ( sizeof(int4) * 2 != sizeof(float8) )
{
printf("Error");
return 1;
}

PGconn * conn = PQconnectdb("dbname=test host=localhost user=trusted");
PGresult * res;

PQclear( PQexec(conn, "begin; declare my_cur binary cursor for
select 123.123;") );
res = PQexec(conn,"fetch 1 from my_cur");

float8 dfVal;
float8 dfOrig = 123.123;

union
{
float8 f;
int4 n[2];
} swap;

memcpy(&(swap.n), PQgetvalue( res, 0, 0 ), sizeof(int4) * 2 );

int4 tmp = ntohl(swap.n[0]);
swap.n[0] = ntohl(swap.n[1]);
swap.n[1] = tmp;

dfVal = swap.f;

printf("ret = [%f]\norig = [%f]\n", dfVal, orig);

PQclear(res);
PQfinish(conn);
return 0;
}

Is something wrong?
Thank for any help.