relibc_openlibm/amos/i1mach.f

*DECK I1MACH
      INTEGER FUNCTION I1MACH(I)
C***BEGIN PROLOGUE  I1MACH
C***DATE WRITTEN   750101   (YYMMDD)
C***REVISION DATE  890213   (YYMMDD)
C***CATEGORY NO.  R1
C***KEYWORDS  LIBRARY=SLATEC,TYPE=INTEGER(I1MACH-I),MACHINE CONSTANTS
C***AUTHOR  FOX, P. A., (BELL LABS)
C           HALL, A. D., (BELL LABS)
C           SCHRYER, N. L., (BELL LABS)
C***PURPOSE  Returns integer machine dependent constants
C***DESCRIPTION
C
C     I1MACH can be used to obtain machine-dependent parameters
C     for the local machine environment.  It is a function
C     subroutine with one (input) argument, and can be called
C     as follows, for example
C
C          K = I1MACH(I)
C
C     where I=1,...,16.  The (output) value of K above is
C     determined by the (input) value of I.  The results for
C     various values of I are discussed below.
C
C  I/O unit numbers.
C    I1MACH( 1) = the standard input unit.
C    I1MACH( 2) = the standard output unit.
C    I1MACH( 3) = the standard punch unit.
C    I1MACH( 4) = the standard error message unit.
C
C  Words.
C    I1MACH( 5) = the number of bits per integer storage unit.
C    I1MACH( 6) = the number of characters per integer storage unit.
C
C  Integers.
C    assume integers are represented in the S-digit, base-A form
C
C               sign ( X(S-1)*A**(S-1) + ... + X(1)*A + X(0) )
C
C               where 0 .LE. X(I) .LT. A for I=0,...,S-1.
C    I1MACH( 7) = A, the base.
C    I1MACH( 8) = S, the number of base-A digits.
C    I1MACH( 9) = A**S - 1, the largest magnitude.
C
C  Floating-Point Numbers.
C    Assume floating-point numbers are represented in the T-digit,
C    base-B form
C               sign (B**E)*( (X(1)/B) + ... + (X(T)/B**T) )
C
C               where 0 .LE. X(I) .LT. B for I=1,...,T,
C               0 .LT. X(1), and EMIN .LE. E .LE. EMAX.
C    I1MACH(10) = B, the base.
C
C  Single-Precision
C    I1MACH(11) = T, the number of base-B digits.
C    I1MACH(12) = EMIN, the smallest exponent E.
C    I1MACH(13) = EMAX, the largest exponent E.
C
C  Double-Precision
C    I1MACH(14) = T, the number of base-B digits.
C    I1MACH(15) = EMIN, the smallest exponent E.
C    I1MACH(16) = EMAX, the largest exponent E.
C
C  To alter this function for a particular environment,
C  the desired set of DATA statements should be activated by
C  removing the C from column 1.  Also, the values of
C  I1MACH(1) - I1MACH(4) should be checked for consistency
C  with the local operating system.
C
C***REFERENCES  FOX P.A., HALL A.D., SCHRYER N.L.,*FRAMEWORK FOR A
C                 PORTABLE LIBRARY*, ACM TRANSACTIONS ON MATHEMATICAL
C                 SOFTWARE, VOL. 4, NO. 2, JUNE 1978, PP. 177-188.
C***ROUTINES CALLED  (NONE)
C***END PROLOGUE  I1MACH
C
      INTEGER IMACH(16),OUTPUT
      SAVE IMACH
      EQUIVALENCE (IMACH(4),OUTPUT)
C
C     MACHINE CONSTANTS FOR THE IBM PC
C
      DATA IMACH( 1) /     5 /
      DATA IMACH( 2) /     6 /
      DATA IMACH( 3) /     0 /
      DATA IMACH( 4) /     0 /
      DATA IMACH( 5) /    32 /
      DATA IMACH( 6) /     4 /
      DATA IMACH( 7) /     2 /
      DATA IMACH( 8) /    31 /
      DATA IMACH( 9) / 2147483647 /
      DATA IMACH(10) /     2 /
      DATA IMACH(11) /    24 /
      DATA IMACH(12) /  -125 /
      DATA IMACH(13) /   127 /
      DATA IMACH(14) /    53 /
      DATA IMACH(15) / -1021 /
      DATA IMACH(16) /  1023 /
C
C***FIRST EXECUTABLE STATEMENT  I1MACH
      IF (I .LT. 1  .OR.  I .GT. 16) GO TO 10
C
      I1MACH = IMACH(I)
      RETURN
C
   10 CONTINUE
      WRITE (UNIT = OUTPUT, FMT = 9000)
 9000 FORMAT ('1ERROR    1 IN I1MACH - I OUT OF BOUNDS')
C
C     CALL FDUMP
C
C
      STOP
      END