Flonums
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   A "flonum" represents a floating point number.  The translation is
indirect: a decimal floating point number from the text is converted by
`as' to a generic binary floating point number of more than sufficient
precision.  This generic floating point number is converted to a
particular computer's floating point format (or formats) by a portion
of `as' specialized to that computer.

   A flonum is written by writing (in order)
   * The digit `0'.

   * A letter, to tell `as' the rest of the number is a flonum.  `e' is
     recommended.  Case is not important.  On the AMD 29K and H8/300
     architectures, the letter must be: One of the letters `DFPRSX' (in
     upper or lower case).  On the Intel 960 architecture, the letter
     must be: One of the letters `DFT' (in upper or lower case).

   * An optional sign: either `+' or `-'.

   * An optional "integer part": zero or more decimal digits.

   * An optional "fractional part": `.' followed by zero or more
     decimal digits.

   * An optional exponent, consisting of:
        * An `E' or `e'.

        * Optional sign: either `+' or `-'.

        * One or more decimal digits.

   At least one of the integer part or the fractional part must be
present.  The floating point number has the usual base-10 value.

   `as' does all processing using integers.  Flonums are computed
independently of any floating point hardware in the computer running
`as'.