[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[no subject]

    Date: 21 November 1979 17:54-EST
    From: David A. Moon <MOON at MIT-MC>
    Subject: lisp; new recent
    To: BUG-LISP at MIT-MC
    cc: MOON at MIT-MC

	. . . 
    LOAD-BYTE and DEPOSIT-BYTE do not work exactly as documented.  The
    documentation needs to make clear that the bit position is the number
    of the high-order bit counting from LEFT TO RIGHT, i.e. the number of
    bits to the left of the byte IN A FIXNUM.  Better than this crockish
    machine-dependency would be to number the bits from right to left in
    the standard way, as LDB and DPB do, avoiding dependency on machine
    word-length.  Consider what LOAD-BYTE and DEPOSIT-BYTE would do in NIL.

I've inserted the following into the documentation for LOAD-BYTE
         As in standard PDP10 terminology, bits are numbered from high-order
	 to low-order ("left-to-right") with the high-order bit being 0.
The idea here is that a fixnum is being used as a mini bit string.
In NIL, the correspondent, BITS's, would definitely be numbered from
left to right, and there may still be the need to have some "mini bit
string" capability for FIXNUMs (no consing, etc).
    However, you may be looking at the question in the wrong light - there
is no more of a machine-dependency in the scheme which "counts" from the left 
than in one which "counts" from the right.  Both are equally limited
by the wordsize of the machine.