Dear Denis, On Sat, Feb 27, 2010 at 09:22:53PM +0100, Denis Barbier wrote: > > This was fantastic analysis. I actually would like to know how you > > zeroed in onto zdrot to find the problem. > > Hi, > > I used brute force ;) > libblas3gf 1.2-4 is installed on my system, object files from > libblas3gf 1.2-3 have been unpacked into dir1, half files are moved > into dir2. then I compiled > gfortran zgesvd_ex.o dir1/*.o -llapack > and by dichotomy found which object file is causing trouble.
Thanks for letting me know; I shall try to use this method the next time. > > I shall now try to play around with zdrot to see if I can create a > > test case which reproduces the bug, so that I can file a bug report > > with GCC. > > I am afraid that this is not easy, and anyway GCC folks will discard > your bugreport since this bug has been fixed in 4.5. But I am very > interested to know the exact reason, and if there is a way to prevent > this bug by modifying source files. I have been trying, but I am unable to produce errors with my analysis of zdrot individually. In the hope that someone else smarter than me, can find a non-functional test case, I attach my source code. Compiling it with make, and then make FFLAGS=-O3 should result in some difference when the resulting executable is run for some test cases, but which test case it is, I am unsure. HTH, and thanks. Kumar -- Life's errors cry for the merciful beauty that can modulate their isolation into a harmony with the whole. - Rabindranath Tagore (Fireflies, 1928)
CFLAGS ?= -O2
FFLAGS ?= -O2
all: zdrot_test
zdrot_test: zdrot.o zdrot_test.o
zdrot.o: zdrot.f
gfortran -c $(FFLAGS) $< -o $@
zdrot_test.o: zdrot_test.c
$(CC) -c $(CFLAGS) $< -o $@
.PHONY: clean
clean:
$(RM) zdrot_test.o zdrot.o zdrot_test
SUBROUTINE ZDROT( N, CX, INCX, CY, INCY, C, S )
*
* .. Scalar Arguments ..
INTEGER INCX, INCY, N
DOUBLE PRECISION C, S
* ..
* .. Array Arguments ..
COMPLEX*16 CX( * ), CY( * )
* ..
*
* Purpose
* =======
*
* Applies a plane rotation, where the cos and sin (c and s) are real
* and the vectors cx and cy are complex.
* jack dongarra, linpack, 3/11/78.
*
* Arguments
* ==========
*
* N (input) INTEGER
* On entry, N specifies the order of the vectors cx and cy.
* N must be at least zero.
* Unchanged on exit.
*
* CX (input) COMPLEX*16 array, dimension at least
* ( 1 + ( N - 1 )*abs( INCX ) ).
* Before entry, the incremented array CX must contain the n
* element vector cx. On exit, CX is overwritten by the updated
* vector cx.
*
* INCX (input) INTEGER
* On entry, INCX specifies the increment for the elements of
* CX. INCX must not be zero.
* Unchanged on exit.
*
* CY (input) COMPLEX*16 array, dimension at least
* ( 1 + ( N - 1 )*abs( INCY ) ).
* Before entry, the incremented array CY must contain the n
* element vector cy. On exit, CY is overwritten by the updated
* vector cy.
*
* INCY (input) INTEGER
* On entry, INCY specifies the increment for the elements of
* CY. INCY must not be zero.
* Unchanged on exit.
*
* C (input) DOUBLE PRECISION
* On entry, C specifies the cosine, cos.
* Unchanged on exit.
*
* S (input) DOUBLE PRECISION
* On entry, S specifies the sine, sin.
* Unchanged on exit.
*
* =====================================================================
*
* .. Local Scalars ..
INTEGER I, IX, IY
COMPLEX*16 CTEMP
* ..
* .. Executable Statements ..
*
IF( N.LE.0 )
$ RETURN
IF( INCX.EQ.1 .AND. INCY.EQ.1 )
$ GO TO 20
*
* code for unequal increments or equal increments not equal
* to 1
*
IX = 1
IY = 1
IF( INCX.LT.0 )
$ IX = ( -N+1 )*INCX + 1
IF( INCY.LT.0 )
$ IY = ( -N+1 )*INCY + 1
DO 10 I = 1, N
CTEMP = C*CX( IX ) + S*CY( IY )
CY( IY ) = C*CY( IY ) - S*CX( IX )
CX( IX ) = CTEMP
IX = IX + INCX
IY = IY + INCY
10 CONTINUE
RETURN
*
* code for both increments equal to 1
*
20 CONTINUE
DO 30 I = 1, N
CTEMP = C*CX( I ) + S*CY( I )
CY( I ) = C*CY( I ) - S*CX( I )
CX( I ) = CTEMP
30 CONTINUE
RETURN
END
#include <stdio.h>
#include <math.h>
typedef struct _dcomplex {
double real;
double imag;
} dcomplex;
int
zdrot_(int *N, dcomplex *CX, int *INCX, dcomplex *CY,int *INCY, double *C, double *S);
int
main(void)
{
int i;
int n = 5;
dcomplex cx[] = {{1.0, 1.0}, {2.0, 2.0}, {3.0, 3.0}, {4.0, 4.0}, {5.0, 5.0}, {1.0, 1.0}, {2.0, 2.0}, {3.0, 3.0}, {4.0, 4.0}};
int incx = 2;
dcomplex cy[] = {{-5.0, 5.0}, {0.0, 0.0}, {-4.0, 4.0}, {0.0, 0.0}, {-3.0, 3.0}, {0.0, 0.0}, {-2.0, 2.0}, {0.0, 0.0}, {-1.0, 1.0}};
int incy = -2;
double c = 0.5;
double s = sqrt(3.0) / 2.0;
zdrot_(&n, cx, &incx, cy, &incy, &c, &s);
printf("x: {");
for (i = 0; i < n - 1; ++i) {
printf("(%.4f, %.4f), ", cx[2 * i].real, cx[2 * i].imag);
}
printf("(%.4f, %.4f)}\n", cx[2 * (n - 1)].real, cx[2 * (n - 1)].imag);
printf("y: {");
for (i = 0; i < n - 1; ++i) {
printf("(%.4f, %.4f), ", cy[2 * i].real, cy[2 * i].imag);
}
printf("(%.4f, %.4f)}\n", cy[2 * (n - 1)].real, cy[2 * (n - 1)].imag);
return 0;
}
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