98 lines
3.3 KiB
Fortran
98 lines
3.3 KiB
Fortran
*DECK D1MACH
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DOUBLE PRECISION FUNCTION D1MACH(I)
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C***BEGIN PROLOGUE D1MACH
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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=DOUBLE PRECISION(R1MACH-S D1MACH-D),
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C 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 double precision machine dependent constants
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C***DESCRIPTION
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C
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C D1MACH 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 subprogram 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 D = D1MACH(I)
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C
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C where I=1,...,5. The (output) value of D 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 D1MACH( 1) = B**(EMIN-1), the smallest positive magnitude.
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C D1MACH( 2) = B**EMAX*(1 - B**(-T)), the largest magnitude.
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C D1MACH( 3) = B**(-T), the smallest relative spacing.
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C D1MACH( 4) = B**(1-T), the largest relative spacing.
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C D1MACH( 5) = LOG10(B)
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C
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C Assume double precision numbers are represented in the T-digit,
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C base-B form
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C
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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, 0 .LT. X(1), and
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C EMIN .LE. E .LE. EMAX.
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C
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C The values of B, T, EMIN and EMAX are provided in I1MACH as
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C follows:
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C I1MACH(10) = B, the base.
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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 D1MACH(1) - D1MACH(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 XERROR
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C***END PROLOGUE D1MACH
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C
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INTEGER SMALL(4)
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INTEGER LARGE(4)
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INTEGER RIGHT(4)
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INTEGER DIVER(4)
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INTEGER LOG10(4)
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C
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DOUBLE PRECISION DMACH(5)
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SAVE DMACH
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C
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C EQUIVALENCE (DMACH(1),SMALL(1))
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C EQUIVALENCE (DMACH(2),LARGE(1))
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C EQUIVALENCE (DMACH(3),RIGHT(1))
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C EQUIVALENCE (DMACH(4),DIVER(1))
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C EQUIVALENCE (DMACH(5),LOG10(1))
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C
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C MACHINE CONSTANTS FOR THE IBM PC
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C ASSUMES THAT ALL ARITHMETIC IS DONE IN DOUBLE PRECISION
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C ON 8088, I.E., NOT IN 80 BIT FORM FOR THE 8087.
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C
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DATA DMACH(1) / 2.23D-308 /
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C DATA SMALL(1),SMALL(2) / 2002288515, 1050897 /
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DATA DMACH(2) / 1.79D-308 /
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C DATA LARGE(1),LARGE(2) / 1487780761, 2146426097 /
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DATA DMACH(3) / 1.11D-16 /
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C DATA RIGHT(1),RIGHT(2) / -1209488034, 1017118298 /
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DATA DMACH(4) / 2.22D-16 /
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C DATA DIVER(1),DIVER(2) / -1209488034, 1018166874 /
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DATA DMACH(5) / 0.3010299956639812 /
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C DATA LOG10(1),LOG10(2) / 1352628735, 1070810131 /
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C
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C
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C***FIRST EXECUTABLE STATEMENT D1MACH
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IF (I .LT. 1 .OR. I .GT. 5)
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1 CALL XERROR ('D1MACH -- I OUT OF BOUNDS', 25, 1, 2)
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C
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D1MACH = DMACH(I)
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RETURN
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C
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END
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