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38581db0c   daniau   git-svn-id: https... 
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  !DECK R1MACH
        REAL FUNCTION R1MACH (I)
        IMPLICIT NONE
        INTEGER :: I
        REAL :: B, X
  !***BEGIN PROLOGUE  R1MACH
  !***PURPOSE  Return floating point machine dependent constants.
  !***LIBRARY   SLATEC
  !***CATEGORY  R1
  !***TYPE      SINGLE PRECISION (R1MACH-S, D1MACH-D)
  !***KEYWORDS  MACHINE CONSTANTS
  !***AUTHOR  Fox, P. A., (Bell Labs)
  !           Hall, A. D., (Bell Labs)
  !           Schryer, N. L., (Bell Labs)
  !***DESCRIPTION
  !
  !   R1MACH can be used to obtain machine-dependent parameters for the
  !   local machine environment.  It is a function subprogram with one
  !   (input) argument, and can be referenced as follows:
  !
  !        A = R1MACH(I)
  !
  !   where I=1,...,5.  The (output) value of A above is determined by
  !   the (input) value of I.  The results for various values of I are
  !   discussed below.
  !
  !   R1MACH(1) = B**(EMIN-1), the smallest positive magnitude.
  !   R1MACH(2) = B**EMAX*(1 - B**(-T)), the largest magnitude.
  !   R1MACH(3) = B**(-T), the smallest relative spacing.
  !   R1MACH(4) = B**(1-T), the largest relative spacing.
  !   R1MACH(5) = LOG10(B)
  !
  !   Assume single precision numbers are represented in the T-digit,
  !   base-B form
  !
  !              sign (B**E)*( (X(1)/B) + ... + (X(T)/B**T) )
  !
  !   where 0 .LE. X(I) .LT. B for I=1,...,T, 0 .LT. X(1), and
  !   EMIN .LE. E .LE. EMAX.
  !
  !   The values of B, T, EMIN and EMAX are provided in I1MACH as
  !   follows:
  !   I1MACH(10) = B, the base.
  !   I1MACH(11) = T, the number of base-B digits.
  !   I1MACH(12) = EMIN, the smallest exponent E.
  !   I1MACH(13) = EMAX, the largest exponent E.
  !
  !
  !***REFERENCES  P. A. Fox, A. D. Hall and N. L. Schryer, Framework for
  !                 a portable library, ACM Transactions on Mathematical
  !                 Software 4, 2 (June 1978), pp. 177-188.
  !***ROUTINES CALLED  XERMSG
  !***REVISION HISTORY  (YYMMDD)
  !   790101  DATE WRITTEN
  !   960329  Modified for Fortran 90 (BE after suggestions by EG)      
  !***END PROLOGUE  R1MACH
  !      
        X = 1.0
        B = RADIX(X)
        SELECT CASE (I)
          CASE (1)
            R1MACH = B**(MINEXPONENT(X)-1) ! the smallest positive magnitude.
          CASE (2)
            R1MACH = HUGE(X)               ! the largest magnitude.
          CASE (3)
            R1MACH = B**(-DIGITS(X))       ! the smallest relative spacing.
          CASE (4)
            R1MACH = B**(1-DIGITS(X))      ! the largest relative spacing.
          CASE (5)
            R1MACH = LOG10(B)
          CASE DEFAULT
            WRITE (*, FMT = 9000)
   9000     FORMAT ('1ERROR    1 IN R1MACH - I OUT OF BOUNDS')
            STOP
        END SELECT
        RETURN
        END