share/odepack/fortran/dumach.f

   1 *DECK DUMACH
   2       DOUBLE PRECISION FUNCTION DUMACH ()
   3 C***BEGIN PROLOGUE  DUMACH
   4 C***PURPOSE  Compute the unit roundoff of the machine.
   5 C***CATEGORY  R1
   6 C***TYPE      DOUBLE PRECISION (RUMACH-S, DUMACH-D)
   7 C***KEYWORDS  MACHINE CONSTANTS
   8 C***AUTHOR  Hindmarsh, Alan C., (LLNL)
   9 C***DESCRIPTION
  10 C *Usage:
  11 C        DOUBLE PRECISION  A, DUMACH
  12 C        A = DUMACH()
  13 C
  14 C *Function Return Values:
  15 C     A : the unit roundoff of the machine.
  16 C
  17 C *Description:
  18 C     The unit roundoff is defined as the smallest positive machine
  19 C     number u such that  1.0 + u .ne. 1.0.  This is computed by DUMACH
  20 C     in a machine-independent manner.
  21 C
  22 C***REFERENCES  (NONE)
  23 C***ROUTINES CALLED  DUMSUM
  24 C***REVISION HISTORY  (YYYYMMDD)
  25 C   19930216  DATE WRITTEN
  26 C   19930818  Added SLATEC-format prologue.  (FNF)
  27 C   20030707  Added DUMSUM to force normal storage of COMP.  (ACH)
  28 C***END PROLOGUE  DUMACH
  29 C
  30       DOUBLE PRECISION U, COMP
  31 C***FIRST EXECUTABLE STATEMENT  DUMACH
  32       U = 1.0D0
  33  10   U = U*0.5D0
  34       CALL DUMSUM(1.0D0, U, COMP)
  35       IF (COMP .NE. 1.0D0) GO TO 10
  36       DUMACH = U*2.0D0
  37       RETURN
  38 C----------------------- End of Function DUMACH ------------------------
  39       END