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* [Bug c/97365] New: gcvt and qgcvt do not always provide requested precision
@ 2020-10-11 3:14 sisyphus359 at gmail dot com
2020-10-12 6:25 ` [Bug c/97365] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: sisyphus359 at gmail dot com @ 2020-10-11 3:14 UTC (permalink / raw)
To: gcc-bugs
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
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug c/97365] gcvt and qgcvt do not always provide requested precision
2020-10-11 3:14 [Bug c/97365] New: gcvt and qgcvt do not always provide requested precision sisyphus359 at gmail dot com
@ 2020-10-12 6:25 ` rguenth at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-10-12 6:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97365
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
This isn't a problem in the compiler but the used C library. Please report the
issue there.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2020-10-11 3:14 [Bug c/97365] New: gcvt and qgcvt do not always provide requested precision sisyphus359 at gmail dot com
2020-10-12 6:25 ` [Bug c/97365] " rguenth at gcc dot gnu.org
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