https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98201
Bug ID: 98201
Summary: CSQRT function gives bad resuts at runtime
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: pozar at ecs dot umass.edu
Target Milestone: ---
I am running mingw gfortran 9.2.0 on Windows 7, and have a problem with results
from the CSQRT function during runtime. Sample code below, with results.
Starting with a complex argument having increasingly large real part, and a
relatively small imaginary part, csqrt initially gives a correct result (as
tested by squaring the result from CSQRT). But the second row shows some
significant error, and later rows show 'Infinity' for the imaginary part.
(using sq = z**.5 gives correct results)
F95 CODE;
! test CSQRT
complex z, sq
write(6,*) " Argument SquareRoot SR
squared"
do n=1,9
z=-10.**n+(0.,.1)
sq=csqrt(z)
write(*,1) z, sq, sq*sq
end do
1 format(3("(",e10.4,2x,e10.4,")",3x))
pause
RESULTS:
Argument SquareRoot SR squared
(-.1000E+02 0.1000E+00) (0.1581E-01 0.3163E+01) (-.1001E+02 0.1000E+00)
(-.1000E+03 0.1000E+00) (0.5167E-02 0.9676E+01) (-.9362E+02 0.1000E+00)
(-.1000E+04 0.1000E+00) (0.0000E+00 Infinity) ( -Infinity NaN)
(-.1000E+05 0.1000E+00) (0.0000E+00 Infinity) ( -Infinity NaN)
(-.1000E+06 0.1000E+00) (0.0000E+00 Infinity) ( -Infinity NaN)
(-.1000E+07 0.1000E+00) (0.0000E+00 Infinity) ( -Infinity NaN)
(-.1000E+08 0.1000E+00) (0.0000E+00 Infinity) ( -Infinity NaN)
(-.1000E+09 0.1000E+00) (0.0000E+00 Infinity) ( -Infinity NaN)
(-.1000E+10 0.1000E+00) (0.0000E+00 Infinity) ( -Infinity NaN)
PAUSE
