From 81d28e7b13617eba42ef44062442a0500ba121bb Mon Sep 17 00:00:00 2001
From: Simon Maertens <simon@slmaertens.dev>
Date: Wed, 22 Jul 2026 16:40:10 +0200
Subject: [PATCH] Avoid computing ONE / HUGE(ZERO) unless it is needed.  Some
 compilers (e.g., flang) warn about underflow when folding the expression.

---
 INSTALL/dlamch.f | 9 +++++----
 INSTALL/slamch.f | 9 +++++----
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/INSTALL/dlamch.f b/INSTALL/dlamch.f
index e151db4a2..8719e42fa 100644
--- a/INSTALL/dlamch.f
+++ b/INSTALL/dlamch.f
@@ -83,7 +83,7 @@
       PARAMETER          ( ONE = 1.0D+0, ZERO = 0.0D+0 )
 *     ..
 *     .. Local Scalars ..
-      DOUBLE PRECISION   RND, EPS, SFMIN, SMALL, RMACH
+      DOUBLE PRECISION   RND, EPS, SFMIN, SMALL, HUGEVAL, RMACH
 *     ..
 *     .. External Functions ..
       LOGICAL            LSAME
@@ -110,8 +110,9 @@
          RMACH = EPS
       ELSE IF( LSAME( CMACH, 'S' ) ) THEN
          SFMIN = TINY(ZERO)
-         SMALL = ONE / HUGE(ZERO)
-         IF( SMALL.GE.SFMIN ) THEN
+         HUGEVAL = HUGE(ZERO)
+         IF( HUGEVAL*SFMIN.LE.ONE ) THEN
+            SMALL = ONE / HUGEVAL
 *
 *           Use SMALL plus a bit, to avoid the possibility of rounding
 *           causing overflow when computing  1/sfmin.
@@ -130,7 +131,7 @@
       ELSE IF( LSAME( CMACH, 'M' ) ) THEN
          RMACH = MINEXPONENT(ZERO)
       ELSE IF( LSAME( CMACH, 'U' ) ) THEN
-         RMACH = tiny(zero)
+         RMACH = TINY(ZERO)
       ELSE IF( LSAME( CMACH, 'L' ) ) THEN
          RMACH = MAXEXPONENT(ZERO)
       ELSE IF( LSAME( CMACH, 'O' ) ) THEN
diff --git a/INSTALL/slamch.f b/INSTALL/slamch.f
index 1fd9f1533..5f7ffbeb5 100644
--- a/INSTALL/slamch.f
+++ b/INSTALL/slamch.f
@@ -82,7 +82,7 @@
       PARAMETER          ( ONE = 1.0E+0, ZERO = 0.0E+0 )
 *     ..
 *     .. Local Scalars ..
-      REAL               RND, EPS, SFMIN, SMALL, RMACH
+      REAL               RND, EPS, SFMIN, SMALL, HUGEVAL, RMACH
 *     ..
 *     .. External Functions ..
       LOGICAL            LSAME
@@ -109,8 +109,9 @@
          RMACH = EPS
       ELSE IF( LSAME( CMACH, 'S' ) ) THEN
          SFMIN = TINY(ZERO)
-         SMALL = ONE / HUGE(ZERO)
-         IF( SMALL.GE.SFMIN ) THEN
+         HUGEVAL = HUGE(ZERO)
+         IF( HUGEVAL*SFMIN.LE.ONE ) THEN
+            SMALL = ONE / HUGEVAL
 *
 *           Use SMALL plus a bit, to avoid the possibility of rounding
 *           causing overflow when computing  1/sfmin.
@@ -129,7 +130,7 @@
       ELSE IF( LSAME( CMACH, 'M' ) ) THEN
          RMACH = MINEXPONENT(ZERO)
       ELSE IF( LSAME( CMACH, 'U' ) ) THEN
-         RMACH = tiny(zero)
+         RMACH = TINY(ZERO)
       ELSE IF( LSAME( CMACH, 'L' ) ) THEN
          RMACH = MAXEXPONENT(ZERO)
       ELSE IF( LSAME( CMACH, 'O' ) ) THEN