!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