Horiguchi-san, On Tue, Oct 1, 2019 at 3:41 PM Kyotaro Horiguchi <[email protected]> wrote: > I found a trick seems workable generically (*1). (2.0 * > (PG_INT64_MAX/2 + 1)) will generate the value next to the > PG_INT64_MAX based on some assumptions > (*1). IS_DOUBLE_SAFE_IN_INT64() below would be able to check if > the value can be converted into int64 safely or not.
Thanks for sharing a nice way of checking overflow. I tested your IS_DOUBLE_SAFE_IN_INT64() macro in my environment by the simple code (attached to this email) and confirmed that it appropriately handled the overflow. However, further consideration is needed for different architectures. I attached the modified patch. In the patch, I placed the macro in "src/include/c.h", but this may not be a good choice because c.h is widely included from a lot of files. Do you have any good ideas about its placement? Thanks, Yuya Watari NTT Software Innovation Center [email protected]
#include <stdio.h>
#include <stdint.h>
#include <math.h>
#include <float.h>
#define PG_INT64_MAX INT64_MAX
#define PG_INT64_MIN INT64_MIN
/*
* Check if a double value can be casted into int64.
*
* This macro is assuming that FLT_RADIX == 2 so that the * 2.0 trick works,
* PG_INT64_MAX is so below DBL_MAX that the doubled value can be represented
* in double and DBL_MANT_DIG is equal or smaller than DBL_MAX_EXP so that
* ceil() returns expected result.
*/
#define MIN_DOUBLE_OVER_INT64_MAX (2.0 * (double) (PG_INT64_MAX / 2 + 1))
#define MAX_DOUBLE_UNDER_INT64_MIN (2.0 * (double) (PG_INT64_MIN / 2 - 1))
#if -PG_INT64_MAX != PG_INT64_MIN
#define IS_DOUBLE_SAFE_IN_INT64(x) \
((x) < MIN_DOUBLE_OVER_INT64_MAX && ceil(x) >= (double) PG_INT64_MIN)
#else
#define IS_DOUBLE_SAFE_IN_INT64(x) \
((x) < MIN_DOUBLE_OVER_INT64_MAX && (x) > MAX_DOUBLE_UNDER_INT64_MIN)
#endif
int main()
{
double values[] =
{
-pow(2, 63) - 1025,
-pow(2, 63),
pow(2, 63) - 1024,
pow(2, 63),
INFINITY,
-INFINITY,
NAN
};
for (int i = 0; i < sizeof(values) / sizeof(values[0]); i++)
{
double value = values[i];
printf("value == %lf, Overflow = %s\n", value,
!IS_DOUBLE_SAFE_IN_INT64(value) ? "true" : "false");
}
}
v3-keep-compiler-silence.patch
Description: Binary data
