Force Fortran 77 SIGN semantics viz. negative zero, matching the original algorithm.

Author: matcross

SRC/dlacn2.f

@@ -160,7 +160,7 @@ SUBROUTINE DLACN2( N, V, X, ISGN, EST, KASE, ISAVE )
 * ..
 * .. Local Scalars ..
  INTEGER I, JLAST
- DOUBLE PRECISION ALTSGN, ESTOLD, TEMP
+ DOUBLE PRECISION ALTSGN, ESTOLD, TEMP, XS
 * ..
 * .. External Functions ..
  INTEGER IDAMAX
@@ -199,7 +199,11 @@ SUBROUTINE DLACN2( N, V, X, ISGN, EST, KASE, ISAVE )
  EST = DASUM( N, X, 1 )
 *
  DO 30 I = 1, N
- X( I ) = SIGN( ONE, X( I ) )
+ IF( X(I).GE.ZERO ) THEN
+ X(I) = ONE
+ ELSE
+ X(I) = -ONE
+ END IF
  ISGN( I ) = NINT( X( I ) )
  30 CONTINUE
  KASE = 2
@@ -232,7 +236,12 @@ SUBROUTINE DLACN2( N, V, X, ISGN, EST, KASE, ISAVE )
  ESTOLD = EST
  EST = DASUM( N, V, 1 )
  DO 80 I = 1, N
- IF( NINT( SIGN( ONE, X( I ) ) ).NE.ISGN( I ) )
+ IF( X(I).GE.ZERO ) THEN
+ XS = ONE
+ ELSE
+ XS = -ONE
+ END IF
+ IF( NINT( XS ).NE.ISGN( I ) )
  $ GO TO 90
  80 CONTINUE
 * REPEATED SIGN VECTOR DETECTED, HENCE ALGORITHM HAS CONVERGED.
@@ -244,7 +253,11 @@ SUBROUTINE DLACN2( N, V, X, ISGN, EST, KASE, ISAVE )
  $ GO TO 120
 *
  DO 100 I = 1, N
- X( I ) = SIGN( ONE, X( I ) )
+ IF( X(I).GE.ZERO ) THEN
+ X(I) = ONE
+ ELSE
+ X(I) = -ONE
+ END IF
  ISGN( I ) = NINT( X( I ) )
  100 CONTINUE
  KASE = 2