https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97365
Bug ID: 97365
Summary: gcvt and qgcvt do not always provide requested
precision
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: sisyphus359 at gmail dot com
Target Milestone: ---
gcvt() will assign no more than 17 digits of precision.
qgcvt() will assign no more than 21 digits of precision.
Here is the demo :
/************************************************/
#include <stdio.h>
#include <stdlib.h>
int main(void) {
char ebuf[80];
gcvt(0.1, 55, ebuf);
printf("%s\n", ebuf);
qgcvt(0.1L, 67, ebuf);
printf("%s\n", ebuf);
return 0;
}
/************************************************/
On Ubuntu-20.04, gcc-9.3.0
I got:
0.10000000000000001
0.100000000000000000001
I expected:
0.1000000000000000055511151231257827021181583404541015625
0.1000000000000000000013552527156068805425093160010874271392822265625
The "expected" values are exact base 10 representations of the values contained
in the double 0.1, and in the (80-bit extended precision) long double 0.1.
Cheers,
Rob
