I1MACH(3)

SYNOPSIS
INTEGER FUNCTION I1MACH (I)

NAME
i1mach - 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).