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Avoid computing ONE/HUGE unless needed (Reference-LAPACK PR 1331) #5939

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Merged
martin-frbg merged 1 commit into from
Jul 22, 2026
+10 −8
Merged

Avoid computing ONE/HUGE unless needed (Reference-LAPACK PR 1331) #5939

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9 changes: 5 additions & 4 deletions lapack-netlib/INSTALL/dlamch.f
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,7 @@ DOUBLE PRECISION FUNCTION DLAMCH( CMACH )
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
Expand All @@ -111,8 +111,9 @@ DOUBLE PRECISION FUNCTION DLAMCH( CMACH )
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.
Expand All @@ -131,7 +132,7 @@ DOUBLE PRECISION FUNCTION DLAMCH( CMACH )
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
Expand Down
9 changes: 5 additions & 4 deletions lapack-netlib/INSTALL/slamch.f
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Expand Up @@ -84,7 +84,7 @@ REAL FUNCTION SLAMCH( CMACH )
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
Expand All @@ -111,8 +111,9 @@ REAL FUNCTION SLAMCH( CMACH )
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.
Expand All @@ -131,7 +132,7 @@ REAL FUNCTION SLAMCH( CMACH )
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
Expand Down
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