Francis J. Monari, Esquire <[email protected]> wrote:
> All,
>
> How are +infinity and -infinity handled?
>
> Frank.
Don't forget signed zero, signaling and quiet NaN.
Here is a short c++ programs to show how +infinity, -infinity
zero, -zero, quiet NaN, signaling NaN are internally represented
in IEEE-754:
$ cat double.cpp
#include <limits>
#include <iostream>
#include <cstdint>
using namespace std;
int main()
{
union
{
double d;
uint64_t i;
} inf, ninf, zero, nzero, qnan, snan;
if (numeric_limits<double>::has_infinity)
{
inf.d = numeric_limits<double>::infinity();
ninf.d = -inf.d;
cout << "+infinity:\t[" << inf.d << "]" << "\t0x" << hex <<
inf.i << dec << endl;
cout << "-infinity:\t[" << ninf.d << "]" << "\t0x" << hex <<
ninf.i << dec << endl;
zero.d = 1/inf.d;
nzero.d = 1/ninf.d;
cout << "zero\t\t[" << zero.d << "]" << "\t0x" << hex << zero.i
<< dec << endl;
cout << "-zero\t\t[" << nzero.d << "]" << "\t0x" << hex << nzero.i
<< dec << endl;
}
if (numeric_limits<double>::has_quiet_NaN)
{
qnan.d = numeric_limits<double>::quiet_NaN();
cout << "quiet nan:\t[" << qnan.d << "]" << "\t0x" << hex <<
qnan.i << dec << endl;
}
if (numeric_limits<double>::has_signaling_NaN)
{
snan.d = numeric_limits<double>::signaling_NaN();
cout << "signaling nan:\t[" << snan.d << "]" << "\t0x" << hex <<
snan.i << dec << endl;
}
return 0;
}
$ g++ -std=gnu++0x -Wall double.cpp
$ ./a.out
+infinity: [inf] 0x7ff0000000000000
-infinity: [-inf] 0xfff0000000000000
zero [0] 0x0
-zero [-0] 0x8000000000000000
quiet nan: [nan] 0x7ff8000000000000
signaling nan: [nan] 0x7ffc000000000000
In sqlite:
sqlite> CREATE TABLE t (pos REAL, neg REAL, nn REAL);
sqlite> INSERT into t VALUES (1, 2, 3);
sqlite> .nullvalue ThisIsANull
sqlite> insert into t values ((1e305 * 1e305), (-1e305 * 1e305), 1/0);
sqlite> insert into t values (1/(1e305 * 1e305), 1/(-1e305 * 1e305), 1/0);
spatialite> SELECT * FROM t;
1.0|2.0|3.0
Inf|-Inf|ThisIsANull
0.0|0.0|ThisIsANull
The signed zero seems lost in SQLite.
Regards
-- Dominique
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