Bug 175913
| Summary: | Wrong calculation result with complex SQRT in gfortran | ||
|---|---|---|---|
| Product: | [Fedora] Fedora | Reporter: | Alexander Täschner <taschna> |
| Component: | gcc | Assignee: | Jakub Jelinek <jakub> |
| Status: | CLOSED NOTABUG | QA Contact: | |
| Severity: | high | Docs Contact: | |
| Priority: | medium | ||
| Version: | 4 | ||
| Target Milestone: | --- | ||
| Target Release: | --- | ||
| Hardware: | i386 | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | Bug Fix | |
| Doc Text: | Story Points: | --- | |
| Clone Of: | Environment: | ||
| Last Closed: | 2005-12-16 13:44:28 UTC | Type: | --- |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
The result is certainly the same as with Intel Fortran 9.0 (as well as the same thing rewritten into C). The reason is that: Z1**2 is (4.0d0,0.0d0), but -Z1**2 is (-4.0d0,-0.0d0). And while SQRT((-4.0d0,0.0d0)) is really (0.0d0,2.0d0), SQRT((-4.0d0,-0.0d0)) is (0.0d0,-2.0d0). This is a changed behaviour compared to g77 (3.4.4 20050721 (Red Hat 3.4.4-2)). On Windows the Compaq Visual Fortran 6 gives also the result (0,2). Therefore I am not sure whether it is a bug or not. I came across the bug when testing to compile the CERNLIB. There the math test C208 failed because of the new behaviour. |
The square root of -4.0 should be (0.0,2.0), but in the following test program it gives (0.0,-2.0). For this test the following version of gcc were used: gcc version 4.0.2 20051125 (Red Hat 4.0.2-8). [taschna@localhost ~]$ cat ctest.f PROGRAM CTEST DOUBLE COMPLEX Z1, Z2, Z3 Z1=(2.0d0,0.0d0) Z2=-Z1**2 Z3=SQRT(Z2) WRITE(*,*) 'SQRT((-4.0d0,0.0d0))=', SQRT((-4.0d0,0.0d0)) WRITE(*,*) 'Z2=', Z2 WRITE(*,*) 'Z3=SQRT(Z2)=', Z3 END [taschna@localhost ~]$ gfortran -O0 ctest.f -o ctest;./ctest SQRT((-4.0d0,0.0d0))= ( 0.00000000000000 , 2.00000000000000 ) Z2= ( -4.00000000000000 , 0.00000000000000 ) Z3=SQRT(Z2)= ( 0.00000000000000 , -2.00000000000000 ) The program gives also the wrong result, when DOUBLE COMPLEX is substituted with COMPLEX.