i1mach <- function ( i )

#*****************************************************************************80
#
## I1MACH returns integer machine constants.
#
#  Discussion:
#
#    Input/output 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 <= X(1:S-1) < A.
#
#      I1MACH(7) = A, the base.
#      I1MACH(8) = S, the number of base A digits.
#      I1MACH(9) = A^S-1, the largest integer.
#
#    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 <= X(I) < B for I=1 to T, 0 < X(1) and EMIN <= E <= 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.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    06 February 2020
#
#  Author:
#
#    Original FORTRAN77 version by Phyllis Fox, Andrew Hall, Norman Schryer
#    R version by John Burkardt.
#
#  Reference:
#
#    Phyllis Fox, Andrew Hall, Norman Schryer,
#    Algorithm 528,
#    Framework for a Portable Library,
#    ACM Transactions on Mathematical Software,
#    Volume 4, Number 2, June 1978, page 176-188.
#
#  Input:
#
#    integer I, chooses the parameter to be returned.
#    1 <= I <= 16.
#
#  Output:
#
#    integer VALUE, the value of the chosen parameter.
#
{
  if ( i < 1 )
  {
    cat ( "\n" )
    cat ( "I1MACH - Fatal error!\n" )
    cat ( "  The input argument I is out of bounds.\n" )
    cat ( "  Legal values satisfy 1 <= I <= 16.\n" )
    cat ( "  I =", i, "\n" )
    stop ( "I1MACH - Fatal error!" )
  } else if ( i == 1 ) {
    value <- 5
  } else if ( i == 2 ) {
    value <- 6
  } else if ( i == 3 ) {
    value <- 7
  } else if ( i == 4 ) {
    value <- 6
  } else if ( i == 5 ) {
    value <- 32
  } else if ( i == 6 ) {
    value <- 4
  } else if ( i == 7 ) {
    value <- 2
  } else if ( i == 8 ) {
    value <- 31
  } else if ( i == 9 ) {
    value <- .Machine$integer.max
  } else if ( i == 10 ) {
    value <- 2
  } else if ( i == 11 ) {
    value <- .Machine$double.digits
  } else if ( i == 12 ) {
    value <- .Machine$double.min.exp
  } else if ( i == 13 ) {
    value <- .Machine$double.max.exp
  } else if ( i == 14 ) {
    value <- .Machine$double.digits
  } else if ( i == 15 ) {
    value <- .Machine$double.min.exp
  } else if ( i == 16 ) {
    value <- .Machine$double.max.exp
  } else if ( 16 < i ) {
    cat ( "\n" )
    cat ( "I1MACH - Fatal error!\n" )
    cat ( "  The input argument I is out of bounds.\n" )
    cat ( "  Legal values satisfy 1 <= I <= 16.\n" )
    cat ( "  I = ", i, "\n" )
    stop ( "I1MACH - Fatal error!" )
  }

  return ( value )
}