On Mon, Dec 5, 2016 at 11:14 AM, Dave Wade <dave.g4...@gmail.com> wrote:
> > -----Original Message----- > > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of David > > Bridgham > > Sent: 05 December 2016 18:37 > > To: General Discussion: On-Topic and Off-Topic Posts > > <cctalk@classiccmp.org> > > Subject: Re: Odd "endianness" [was Re: RE: Base 64 posts to the list] > > > > On 12/05/2016 12:17 PM, Chuck Guzis wrote: > > > > > Or how about architectures not using a word length that's an integral > > > number of bytes? > > > > You mean like any 36-bit machine? > > Honeywell L66 & DPS8 used to have 36 bit words which originally contained 6 > x 6-bit characters. > When they extended the machines to work with ASCII they put 4 x 9-bit > characters which I seem to > remember they called 9-bit bytes.. > > Yes; the Extended Instruction set handles 4*9bit, 6*6bit, 8*4bit (with the 4 padding bits scattered through the word). >From memory: PDP-10: 36 bit word, 5*7bit characters. PDP-15: 18 bit word, but it was so long ago, I don't remember.... CDC 6000: 60 bit word, 10 six bit characters. PDP11 "middle endian" see "NUXI problem: http://www.catb.org/jargon/html/M/middle-endian.html PDP11 RADIX-50 3 characters packed into a 16 bit word; each character in a 0:39 set. Back to Der Mouse question re: non-symmetrical mapping.... hton and ntoh are not meant has generalized data conversion; they are intended as network data packet field conversion; the domain of ntohl is a 32bit unsigned integer; the range is a host object larger enough to contain all possible values. For hosts that are base 2 and have word sizes that divide 32bits evenly, the functions would typically be identity or bit rearrangement, and the htonl and ntohl functions would be symmetric -- I suspect that a good mathematician could 'prove' that cycle length is always 2 given the constraints. Cases like 36 bits words mean that htonl is "lossy"; it throws away bits and and ntohl pads the result with 0s -- they are not symmetrical, thus the answer to the order-2 cycle question is 'not applicable' -- Charles
