Bug 189 - cblat1 test fails
: cblat1 test fails
Product: Eigen
Classification: Unclassified
Component: General
: 3.0
: All All
: --- normal
Assigned To: Nobody
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Reported: 2011-02-18 12:52 UTC by Jitse Niesen
Modified: 2011-02-18 15:08 UTC (History)
2 users (show)


Description Jitse Niesen 2011-02-18 12:52:32 UTC
The clat1 test fails on my computer. This is with both gcc 4.1 and 4.3, both
with and without SSE, and both Debug and Release mode. On the other hand, the
test succeeds on Gael's computer. All other BLAS tests work.

The problem seems to be in the interface of Fortran with C code. The following
GDB session shows that the arguments are correct when Fortran calls the C
function cdotc(), but when I step into cdotc(), the arguments are shifted.

My first guess would be that the issue is the COMPLEX return value of CDOTC.
The cblat1 test seems to be the only test that covers a BLAS function returning
a COMPLEX and there are apparently different calling conventions in this case,
see http://gcc.gnu.org/onlinedocs/gfortran/Code-Gen-Options.html

I checked that the Fortran and C++ compiler have the same version number. I did
not set any flags for the Fortran compiler.

GDB session

(gdb) break cblat1.f:493
Breakpoint 1 at 0x804967d: file
/home/amsta/jitse/scratch/eigen-official/blas/testing/cblat1.f, line 493.
(gdb) run
Starting program:
 Complex BLAS Test Program Results

 Test of subprogram number  1            CDOTC

Breakpoint 1, check2 (sfac=@0x804b880)
    at /home/amsta/jitse/scratch/eigen-official/blas/testing/cblat1.f:493
493                    CDOT(1) = CDOTC(N,CX,INCX,CY,INCY)
Current language:  auto; currently fortran
(gdb) print N
$1 = 0
(gdb) print INCX
$2 = 1
(gdb) print INCY
$3 = 1
(gdb) print &N
$4 = (PTR TO -> ( integer(kind=4) )) 0x804ce44
(gdb) print &CX
$5 = (PTR TO -> ( complex(kind=4) (7))) 0xbfb1e080
(gdb) print &INCX
$6 = (PTR TO -> ( integer(kind=4) )) 0x804ce48
(gdb) print &CY
$7 = (PTR TO -> ( complex(kind=4) (7))) 0xbfb1e048
(gdb) print &INCY
$8 = (PTR TO -> ( integer(kind=4) )) 0x804ce4c
(gdb) step
cdotc_ (n=0xbfb1e080, px=0x804ce48, incx=0xbfb1e048, py=0x804ce4c,
    at /home/amsta/jitse/scratch/eigen-official/blas/level1_cplx_impl.h:59
59        if(*n<=0) return 0;
Current language:  auto; currently c++
Comment 1 Gael Guennebaud 2011-02-18 14:45:37 UTC
Indeed, there are various conventions to return COMPLEX. The safest is to
simply write a small fortran wrapper to CDOTC calling a version returning the
result in an argument.

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