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Avoid intermediate overflow in ?LARFGP (Reference-LAPACK PR 1290) #5886

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Merged
martin-frbg merged 2 commits into from
Jul 6, 2026
+13 −4
Merged

Avoid intermediate overflow in ?LARFGP (Reference-LAPACK PR 1290) #5886

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f3f5fd9
Avoid intermediate overflow (Reference-LAPACK PR 1290)
martin-frbg Jul 5, 2026
022b1c6
Merge branch 'OpenMathLib:develop' into lapack1290
martin-frbg Jul 5, 2026
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10 changes: 7 additions & 3 deletions lapack-netlib/SRC/dlarfgp.f
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Original file line number Diff line number Diff line change
Expand Up @@ -5,15 +5,13 @@
* Online html documentation available at
* http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download DLARFGP + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlarfgp.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlarfgp.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlarfgp.f">
*> [TXT]</a>
*> \endhtmlonly
*
* Definition:
* ===========
Expand Down Expand Up @@ -101,6 +99,7 @@
*
* =====================================================================
SUBROUTINE DLARFGP( N, ALPHA, X, INCX, TAU )
IMPLICIT NONE
*
* -- LAPACK auxiliary routine --
* -- LAPACK is a software package provided by Univ. of Tennessee, --
Expand Down Expand Up @@ -221,7 +220,12 @@ SUBROUTINE DLARFGP( N, ALPHA, X, INCX, TAU )
*
* This is the general case.
*
CALL DSCAL( N-1, ONE / ALPHA, X, INCX )
IF( ABS( ALPHA ).LT.SMLNUM ) THEN
CALL DSCAL( N-1, ONE / SMLNUM, X, INCX )
CALL DSCAL( N-1, SMLNUM / ALPHA, X, INCX )
ELSE
CALL DSCAL( N-1, ONE / ALPHA, X, INCX )
END IF
*
END IF
*
Expand Down
7 changes: 6 additions & 1 deletion lapack-netlib/SRC/slarfgp.f
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Expand Up @@ -221,7 +221,12 @@ SUBROUTINE SLARFGP( N, ALPHA, X, INCX, TAU )
*
* This is the general case.
*
CALL SSCAL( N-1, ONE / ALPHA, X, INCX )
IF( ABS( ALPHA ).LT.SMLNUM ) THEN
CALL SSCAL( N-1, ONE / SMLNUM, X, INCX )
CALL SSCAL( N-1, SMLNUM / ALPHA, X, INCX )
ELSE
CALL SSCAL( N-1, ONE / ALPHA, X, INCX )
END IF
*
END IF
*
Expand Down
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