Public bug reported:
On Ubuntu 20.04.1 LTS, glibc-2.31:
gcvt() will output no more than 17 digits of precision.
qgcvt() will output 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;
}
/************************************************/
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.
The same problem existed on Ubuntu-18.04. I expect it is a longstanding
issue
Cheers,
Rob
** Affects: glibc (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1899553
Title:
gcvt and qgcvt do not always provide requested precsion
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