DOUBLE PRECISION FUNCTION PDA_D1MACH (I)
***BEGIN PROLOGUE PDA_D1MACH
***PURPOSE Return floating point machine dependent constants.
***LIBRARY SLATEC
***CATEGORY R1
***TYPE DOUBLE PRECISION (R1MACH-S, PDA_D1MACH-D)
***KEYWORDS MACHINE CONSTANTS
***AUTHOR Fox, P. A., (Bell Labs)
Hall, A. D., (Bell Labs)
Schryer, N. L., (Bell Labs)
***DESCRIPTION
PDA_D1MACH 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:
D = PDA_D1MACH(I)
where I=1,...,5. The (output) value of D above is determined by
the (input) value of I. The results for various values of I are
discussed below.
PDA_D1MACH( 1) = B**(EMIN-1), the smallest positive magnitude.
PDA_D1MACH( 2) = B**EMAX*(1 - B**(-T)), the largest magnitude.
PDA_D1MACH( 3) = B**(-T), the smallest relative spacing.
PDA_D1MACH( 4) = B**(1-T), the largest relative spacing.
PDA_D1MACH( 5) = LOG10(B)
Assume double 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 PDA_I1MACH as
follows:
PDA_I1MACH(10) = B, the base.
PDA_I1MACH(14) = T, the number of base-B digits.
PDA_I1MACH(15) = EMIN, the smallest exponent E.
PDA_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 PDA_D1MACH(1) - PDA_D1MACH(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 PDA_XERMSG
***REVISION HISTORY (YYMMDD)
750101 DATE WRITTEN
890213 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900315 CALLs to XERROR changed to CALLs to PDA_XERMSG. (THJ)
900618 Added DEC RISC constants. (WRB)
900723 Added IBM RS 6000 constants. (WRB)
900911 Added SUN 386i constants. (WRB)
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)
950404 If index out of range, return value zero, but return.
(HME).
***END PROLOGUE PDA_D1MACH
PDA [1ex