◆ dlamc4()

subroutine dlamc4	(	integer	EMIN,
		double precision	START,
		integer	BASE
	)

DLAMC4

Purpose:

 DLAMC4 is a service routine for DLAMC2.

Parameters

[out]

EMIN

          The minimum exponent before (gradual) underflow, computed by
          setting A = START and dividing by BASE until the previous A
          can not be recovered.

[in]

START

          The starting point for determining EMIN.

[in]

BASE

          The base of the machine.

Definition at line 694 of file dlamchf77.f.

 *
 *  -- LAPACK auxiliary routine (version 3.7.0) --
 *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
 *     November 2010
 *
 *     .. Scalar Arguments ..
       INTEGER            BASE, EMIN
       DOUBLE PRECISION   START
 *     ..
 * =====================================================================
 *
 *     .. Local Scalars ..
       INTEGER            I
       DOUBLE PRECISION   A, B1, B2, C1, C2, D1, D2, ONE, RBASE, ZERO
 *     ..
 *     .. External Functions ..
       DOUBLE PRECISION   DLAMC3
       EXTERNAL           dlamc3
 *     ..
 *     .. Executable Statements ..
 *
       a = start
       one = 1
       rbase = one / base
       zero = 0
       emin = 1
       b1 = dlamc3( a*rbase, zero )
       c1 = a
       c2 = a
       d1 = a
       d2 = a
 *+    WHILE( ( C1.EQ.A ).AND.( C2.EQ.A ).AND.
 *    $       ( D1.EQ.A ).AND.( D2.EQ.A )      )LOOP
    10 CONTINUE
       IF( ( c1.EQ.a ) .AND. ( c2.EQ.a ) .AND. ( d1.EQ.a ) .AND.
      $    ( d2.EQ.a ) ) THEN
          emin = emin - 1
          a = b1
          b1 = dlamc3( a / base, zero )
          c1 = dlamc3( b1*base, zero )
          d1 = zero
          DO 20 i = 1, base
             d1 = d1 + b1
    20    CONTINUE
          b2 = dlamc3( a*rbase, zero )
          c2 = dlamc3( b2 / rbase, zero )
          d2 = zero
          DO 30 i = 1, base
             d2 = d2 + b2
    30    CONTINUE
          GO TO 10
       END IF
 *+    END WHILE
 *
       RETURN
 *
 *     End of DLAMC4
 *

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