Handle corner cases of LWORK (Reference-LAPACK PR 942)

lapack-netlib/SRC/cgehrd.f

@@ -89,7 +89,7 @@
 *>
 *> \param[out] WORK
 *> \verbatim
-*>          WORK is COMPLEX array, dimension (LWORK)
+*>          WORK is COMPLEX array, dimension (MAX(1,LWORK))
 *>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
 *> \endverbatim
 *>
@@ -222,13 +222,19 @@
          INFO = -8
       END IF
 *
+      NH = IHI - ILO + 1
       IF( INFO.EQ.0 ) THEN
 *
 *        Compute the workspace requirements
 *
-         NB = MIN( NBMAX, ILAENV( 1, 'CGEHRD', ' ', N, ILO, IHI, -1 ) )
-         LWKOPT = N*NB + TSIZE
-         WORK( 1 ) = SROUNDUP_LWORK(LWKOPT)
+         IF( NH.LE.1 ) THEN
+            LWKOPT = 1
+         ELSE
+            NB = MIN( NBMAX, ILAENV( 1, 'DGEHRD', ' ', N, ILO, IHI,
+     $                              -1 ) )
+            LWKOPT = N*NB + TSIZE
+         END IF
+         WORK( 1 ) = SROUNDUP_LWORK( LWKOPT )
       END IF
 *
       IF( INFO.NE.0 ) THEN
@@ -249,7 +255,6 @@
 *
 *     Quick return if possible
 *
-      NH = IHI - ILO + 1
       IF( NH.LE.1 ) THEN
          WORK( 1 ) = 1
          RETURN
@@ -269,7 +274,7 @@
 *
 *           Determine if workspace is large enough for blocked code
 *
-            IF( LWORK.LT.N*NB+TSIZE ) THEN
+            IF( LWORK.LT.LWKOPT ) THEN
 *
 *              Not enough workspace to use optimal NB:  determine the
 *              minimum value of NB, and reduce NB or force use of
@@ -345,7 +350,8 @@
 *     Use unblocked code to reduce the rest of the matrix
 *
       CALL CGEHD2( N, I, IHI, A, LDA, TAU, WORK, IINFO )
-      WORK( 1 ) = SROUNDUP_LWORK(LWKOPT)
+*
+      WORK( 1 ) = SROUNDUP_LWORK( LWKOPT )
 *
       RETURN
 *