From f3f5fd9116e41a1d6b7a766ee998c34bd0fd7bd0 Mon Sep 17 00:00:00 2001
From: Martin Kroeker <martin@ruby.chemie.uni-freiburg.de>
Date: Sun, 5 Jul 2026 17:43:58 +0200
Subject: [PATCH] Avoid intermediate overflow (Reference-LAPACK PR 1290)

---
 lapack-netlib/SRC/dlarfgp.f | 10 +++++++---
 lapack-netlib/SRC/slarfgp.f |  7 ++++++-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/lapack-netlib/SRC/dlarfgp.f b/lapack-netlib/SRC/dlarfgp.f
index a8cf1b31e3..fe66139977 100644
--- a/lapack-netlib/SRC/dlarfgp.f
+++ b/lapack-netlib/SRC/dlarfgp.f
@@ -5,7 +5,6 @@
 * 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>
@@ -13,7 +12,6 @@
 *> [ZIP]</a>
 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlarfgp.f">
 *> [TXT]</a>
-*> \endhtmlonly
 *
 *  Definition:
 *  ===========
@@ -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,    --
@@ -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
 *
diff --git a/lapack-netlib/SRC/slarfgp.f b/lapack-netlib/SRC/slarfgp.f
index c28274c2c4..ab297f485a 100644
--- a/lapack-netlib/SRC/slarfgp.f
+++ b/lapack-netlib/SRC/slarfgp.f
@@ -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
 *