source: LMDZ6/trunk/libf/misc/i1mach.f90 @ 5319

!DECK I1MACH
INTEGER FUNCTION I1MACH (I)
  IMPLICIT NONE
  !***BEGIN PROLOGUE  I1MACH
  !***PURPOSE  Return integer machine dependent constants.
  !***LIBRARY   SLATEC
  !***CATEGORY  R1
  !***TYPE      INTEGER (I1MACH-I)
  !***KEYWORDS  MACHINE CONSTANTS
  !***AUTHOR  Fox, P. A., (Bell Labs)
        ! Hall, A. D., (Bell Labs)
        ! Schryer, N. L., (Bell Labs)
  !***DESCRIPTION
  !
  !   I1MACH 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:
  !
  !    K = I1MACH(I)
  !
  !   where I=1,...,16.  The (output) value of K above is determined by
  !   the (input) value of I.  The results for various values of I are
  !   discussed below.
  !
  !   I/O unit numbers:
  ! I1MACH( 1) = the standard input unit.
  ! I1MACH( 2) = the standard output unit.
  ! I1MACH( 3) = the standard punch unit.
  ! I1MACH( 4) = the standard error message unit.
  !
  !   Words:
  ! I1MACH( 5) = the number of bits per integer storage unit.
  ! I1MACH( 6) = the number of characters per integer storage unit.
  !
  !   Integers:
  ! assume integers are represented in the S-digit, base-A form
  !
  !            sign ( X(S-1)*A**(S-1) + ... + X(1)*A + X(0) )
  !
  !            where 0 .LE. X(I) .LT. A for I=0,...,S-1.
  ! I1MACH( 7) = A, the base.
  ! I1MACH( 8) = S, the number of base-A digits.
  ! I1MACH( 9) = A**S - 1, the largest magnitude.
  !
  !   Floating-Point Numbers:
  ! Assume floating-point 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.
  ! I1MACH(10) = B, the base.
  !
  !   Single-Precision:
  ! I1MACH(11) = T, the number of base-B digits.
  ! I1MACH(12) = EMIN, the smallest exponent E.
  ! I1MACH(13) = EMAX, the largest exponent E.
  !
  !   Double-Precision:
  ! I1MACH(14) = T, the number of base-B digits.
  ! I1MACH(15) = EMIN, the smallest exponent E.
  ! I1MACH(16) = EMAX, the largest exponent E.
  !
  !   To alter this function for a particular environment, the desired
  !   set of DATA statements should be activated by removing the C from
  !   column 1.  Also, the values of I1MACH(1) - I1MACH(4) should be
  !   checked for consistency with the local operating system.
  !
  !***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  (NONE)
  !***REVISION HISTORY  (YYMMDD)
  !   750101  DATE WRITTEN
  !   891012  Added VAX G-floating constants.  (WRB)
  !   891012  REVISION DATE from Version 3.2
  !   891214  Prologue converted to Version 4.0 format.  (BAB)
  !   900618  Added DEC RISC constants.  (WRB)
  !   900723  Added IBM RS 6000 constants.  (WRB)
  !   901009  Correct I1MACH(7) for IBM Mainframes. Should be 2 not 16.
  !       (RWC)
  !   910710  Added HP 730 constants.  (SMR)
  !   911114  Added Convex IEEE constants.  (WRB)
  !   920121  Added SUN -r8 compiler option constants.  (WRB)
  !   920229  Added Touchstone Delta i860 constants.  (WRB)
  !   920501  Reformatted the REFERENCES section.  (WRB)
  !   920625  Added Convex -p8 and -pd8 compiler option constants.
  !       (BKS, WRB)
  !   930201  Added DEC Alpha and SGI constants.  (RWC and WRB)
  !   930618  Corrected I1MACH(5) for Convex -p8 and -pd8 compiler
  !       options.  (DWL, RWC and WRB).
  !   100623  Use Fortran 95 intrinsic functions (Lionel GUEZ)
  !***END PROLOGUE  I1MACH
  !
  INTEGER :: IMACH(16),OUTPUT
  SAVE IMACH
  EQUIVALENCE (IMACH(4),OUTPUT)
  INTEGER :: I
  !***FIRST EXECUTABLE STATEMENT  I1MACH
  IMACH( 1) =         5
  IMACH( 2) =         6
  IMACH( 3) =         6
  IMACH( 4) =         6
  IMACH( 5) =        bit_size(0)
  IMACH( 6) =         IMACH( 5) / 8
  IMACH( 7) =         radix(0)
  IMACH( 8) =        digits(0)
  IMACH( 9) =     huge(0)
  IMACH(10) =         radix(0.)
  IMACH(11) =        digits(0.)
  IMACH(12) =      minexponent(0.)
  IMACH(13) =       maxexponent(0.)
  IMACH(14) =        digits(0d0)
  IMACH(15) =      minexponent(0d0)
  IMACH(16) =       maxexponent(0d0)
  IF (I .LT. 1  .OR.  I .GT. 16) GO TO 10
  !
  I1MACH = IMACH(I)
  RETURN
  !
   10   CONTINUE
  WRITE (UNIT = OUTPUT, FMT = 9000)
 9000   FORMAT ('1ERROR    1 IN I1MACH - I OUT OF BOUNDS')
  !
  ! CALL FDUMP
  !
  STOP
END FUNCTION I1MACH