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