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Do quick return from LARF1F/LARF1L if C is empty (Reference-LAPACK PR 1435) #6166

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Merged
martin-frbg merged 1 commit into from
Oct 25, 2026
+215 −85
Merged

Do quick return from LARF1F/LARF1L if C is empty (Reference-LAPACK PR 1435) #6166

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4 changes: 4 additions & 0 deletions lapack-netlib/SRC/clarf1f.c
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Original file line number Diff line number Diff line change
Expand Up @@ -418,6 +418,10 @@ static integer c__1 = 1;
--work;

/* Function Body */
/* Quick return if C is empty */
if (*m <= 0 || *n <= 0)
return;

applyleft = lsame_(side, "L");
lastv = 1;
lastc = 0;
Expand Down
28 changes: 19 additions & 9 deletions lapack-netlib/SRC/clarf1f.f
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Expand Up @@ -147,7 +147,7 @@ SUBROUTINE CLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
* ..
* .. Local Scalars ..
LOGICAL APPLYLEFT
INTEGER I, LASTV, LASTC
INTEGER I, J, LASTV, LASTC
* ..
* .. External Subroutines ..
EXTERNAL CAXPY, CGEMV, CGERC, CSCAL
Expand All @@ -161,6 +161,11 @@ SUBROUTINE CLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
EXTERNAL LSAME, ILACLR, ILACLC
* ..
* .. Executable Statements ..
*
* Quick return if C is empty
*
IF( M.LE.0 .OR. N.LE.0 )
$ RETURN
*
APPLYLEFT = LSAME( SIDE, 'L' )
LASTV = 1
Expand Down Expand Up @@ -190,6 +195,11 @@ SUBROUTINE CLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
! Scan for the last non-zero row in C(:,1:lastv).
LASTC = ILACLR(M, LASTV, C, LDC)
END IF
! Set index for V. If INCV < 0, then I points to the end of V.
! For INCV > 0, set I to point to V(2)
IF( INCV.GT.0 ) THEN
I = 1 + INCV
END IF
END IF
IF( LASTC.EQ.0 ) THEN
RETURN
Expand All @@ -208,24 +218,24 @@ SUBROUTINE CLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
* w(1:lastc,1) := C(2:lastv,1:lastc)**H * v(2:lastv,1)
*
CALL CGEMV( 'Conjugate transpose', LASTV - 1, LASTC, ONE,
$ C( 2, 1 ), LDC, V( 1 + INCV ), INCV, ZERO,
$ C( 2, 1 ), LDC, V( I ), INCV, ZERO,
$ WORK, 1 )
*
* w(1:lastc,1) += v(1,1) * C(1,1:lastc)**H
*
DO I = 1, LASTC
WORK( I ) = WORK( I ) + CONJG( C( 1, I ) )
DO J = 1, LASTC
WORK( J ) = WORK( J ) + CONJG( C( 1, J ) )
END DO
*
* C(1, 1:lastc) += - tau * v(1,1) * w(1:lastc,1)**H
*
DO I = 1, LASTC
C( 1, I ) = C( 1, I ) - TAU * CONJG( WORK( I ) )
DO J = 1, LASTC
C( 1, J ) = C( 1, J ) - TAU * CONJG( WORK( J ) )
END DO
*
* C(2:lastv,1:lastc) += - tau * v(2:lastv,1) * w(1:lastc,1)**H
*
CALL CGERC( LASTV - 1, LASTC, -TAU, V( 1 + INCV ), INCV,
CALL CGERC( LASTV - 1, LASTC, -TAU, V( I ), INCV,
$ WORK, 1, C( 2, 1 ), LDC )
END IF
ELSE
Expand All @@ -242,7 +252,7 @@ SUBROUTINE CLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
* w(1:lastc,1) := C(1:lastc,2:lastv) * v(2:lastv,1)
*
CALL CGEMV( 'No transpose', LASTC, LASTV - 1, ONE,
$ C( 1, 2 ), LDC, V( 1 + INCV ), INCV, ZERO,
$ C( 1, 2 ), LDC, V( I ), INCV, ZERO,
$ WORK, 1 )
*
* w(1:lastc,1) += v(1,1) * C(1:lastc,1)
Expand All @@ -256,7 +266,7 @@ SUBROUTINE CLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
* C(1:lastc,2:lastv) += - tau * w(1:lastc,1) * v(2:lastv)**H
*
CALL CGERC( LASTC, LASTV - 1, -TAU, WORK, 1,
$ V( 1 + INCV ), INCV, C( 1, 2 ), LDC )
$ V( I ), INCV, C( 1, 2 ), LDC )
END IF
END IF
RETURN
Expand Down
4 changes: 4 additions & 0 deletions lapack-netlib/SRC/clarf1l.c
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Original file line number Diff line number Diff line change
Expand Up @@ -420,6 +420,10 @@ static integer c__1 = 1;
--work;

/* Function Body */
/* Quick return if C is empty */
if (*m <= 0 || *n <= 0)
return;

applyleft = lsame_(side, "L");
firstv = 1;
lastc = 0;
Expand Down
16 changes: 15 additions & 1 deletion lapack-netlib/SRC/clarf1l.f
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,11 @@ SUBROUTINE CLARF1L( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
EXTERNAL LSAME, ILACLR, ILACLC
* ..
* .. Executable Statements ..
*
* Quick return if C is empty
*
IF( M.LE.0 .OR. N.LE.0 )
$ RETURN
*
APPLYLEFT = LSAME( SIDE, 'L' )
FIRSTV = 1
Expand All @@ -174,7 +179,11 @@ SUBROUTINE CLARF1L( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
ELSE
LASTV = N
END IF
I = 1
IF( INCV.GT.0 ) THEN
I = 1
ELSE
I = 1 - (LASTV-1) * INCV
END IF
! Look for the last non-zero row in V.
DO WHILE( LASTV.GT.FIRSTV .AND. V( I ).EQ.ZERO )
FIRSTV = FIRSTV + 1
Expand All @@ -187,6 +196,11 @@ SUBROUTINE CLARF1L( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
! Scan for the last non-zero row in C(:,1:lastv).
LASTC = ILACLR(M, LASTV, C, LDC)
END IF
! Set index for V. If INCV > 0, then I points to the start of V.
! For INCV < 0, set I to point to V(M-1)
IF( INCV.LT.0 ) THEN
I = 1 - INCV
END IF
END IF
IF( LASTC.EQ.0 ) THEN
RETURN
Expand Down
4 changes: 4 additions & 0 deletions lapack-netlib/SRC/dlarf1f.c
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Original file line number Diff line number Diff line change
Expand Up @@ -413,6 +413,10 @@ static integer c__1 = 1;
--work;

/* Function Body */
/* Quick return if C is empty */
if (*m <= 0 || *n <= 0)
return;

applyleft = lsame_(side, "L");
lastv = 1;
lastc = 0;
Expand Down
18 changes: 14 additions & 4 deletions lapack-netlib/SRC/dlarf1f.f
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Expand Up @@ -188,6 +188,11 @@ SUBROUTINE DLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
EXTERNAL LSAME, ILADLR, ILADLC
* ..
* .. Executable Statements ..
*
* Quick return if C is empty
*
IF( M.LE.0 .OR. N.LE.0 )
$ RETURN
*
APPLYLEFT = LSAME( SIDE, 'L' )
LASTV = 1
Expand Down Expand Up @@ -219,6 +224,11 @@ SUBROUTINE DLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
! Scan for the last non-zero row in C(:,1:lastv).
LASTC = ILADLR(M, LASTV, C, LDC)
END IF
! Set index for V. If INCV < 0, then I points to the end of V.
! For INCV > 0, set I to point to V(2)
IF( INCV.GT.0 ) THEN
I = 1 + INCV
END IF
END IF
IF( LASTC.EQ.0 ) THEN
RETURN
Expand All @@ -240,7 +250,7 @@ SUBROUTINE DLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
*
! w(1:lastc,1) := C(2:lastv,1:lastc)**T * v(2:lastv,1)
CALL DGEMV( 'Transpose', LASTV-1, LASTC, ONE, C(1+1,1),
$ LDC, V(1+INCV), INCV, ZERO, WORK, 1)
$ LDC, V(I), INCV, ZERO, WORK, 1)
! w(1:lastc,1) += C(1,1:lastc)**T * v(1,1) = C(1,1:lastc)**T
CALL DAXPY(LASTC, ONE, C, LDC, WORK, 1)
*
Expand All @@ -250,7 +260,7 @@ SUBROUTINE DLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
! = C(...) - tau * w(1:lastc,1)**T
CALL DAXPY(LASTC, -TAU, WORK, 1, C, LDC)
! C(2:lastv,1:lastc) := C(...) - tau * v(2:lastv,1)*w(1:lastc,1)**T
CALL DGER(LASTV-1, LASTC, -TAU, V(1+INCV), INCV, WORK, 1,
CALL DGER(LASTV-1, LASTC, -TAU, V(I), INCV, WORK, 1,
$ C(1+1,1), LDC)
END IF
ELSE
Expand All @@ -270,7 +280,7 @@ SUBROUTINE DLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
*
! w(1:lastc,1) := C(1:lastc,2:lastv) * v(2:lastv,1)
CALL DGEMV( 'No transpose', LASTC, LASTV-1, ONE,
$ C(1,1+1), LDC, V(1+INCV), INCV, ZERO, WORK, 1 )
$ C(1,1+1), LDC, V(I), INCV, ZERO, WORK, 1 )
! w(1:lastc,1) += C(1:lastc,1) v(1,1) = C(1:lastc,1)
CALL DAXPY(LASTC, ONE, C, 1, WORK, 1)
*
Expand All @@ -280,7 +290,7 @@ SUBROUTINE DLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
! = C(...) - tau * w(1:lastc,1)
CALL DAXPY(LASTC, -TAU, WORK, 1, C, 1)
! C(1:lastc,2:lastv) := C(...) - tau * w(1:lastc,1) * v(2:lastv)**T
CALL DGER( LASTC, LASTV-1, -TAU, WORK, 1, V(1+INCV),
CALL DGER( LASTC, LASTV-1, -TAU, WORK, 1, V(I),
$ INCV, C(1,1+1), LDC )
END IF
END IF
Expand Down
4 changes: 4 additions & 0 deletions lapack-netlib/SRC/dlarf1l.c
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Original file line number Diff line number Diff line change
Expand Up @@ -381,6 +381,10 @@ static integer c__1 = 1;
--work;

/* Function Body */
/* Quick return if C is empty */
if (*m <= 0 || *n <= 0)
return;

applyleft = lsame_(side, "L");
firstv = 1;
lastc = 0;
Expand Down
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