On Fri, 16 Jun 2017 22:56:18 +0100, David W Noon wrote: > >>> In fact, on little-endian systems the numbers are put into big-endian >>> order when loaded into a register. Consequently, these machines do >>> arithmetic in big-endian. >>> >> Ummm... really? > >Yes. > >> I believe IBM computers number bits in a register with >> 0 being the most significant bit; non-IBM computers with 0 being the >> least sighificant bit. I'd call that a bitwise little-endian. And it gives >> an >> easy summation formula for conversion to unsigned integers. > >The endianness is determined by where the MSB and LSB are stored. On IBM >machines the MSB is in the left-most byte of the register and the LSB in >the right-most byte. That is big-endian. > >Ascribing indices to the bit positions in either order makes no >difference. It is the order of *storage* that determines endianness. > ??? We're talking about *registers* here. See your first paragraph I quoted.
What do you mean by "the order of *storage*" of bits in a register other than how one ascribes indices? If I rotate my laptop 180° on my desk, have I swapped the left end and the right end? >The computers perform their arithmetic in whatever byte order the >hardware designers choose. > If they operate serially, it's simplest if they start at the less significant end. >My first system was a clone of an IBM 360. I felt dismay when I first >read a core dump from a PDP-11. > That's one data point confirming my conjecture that people perceive the conventions they learned earliest as Natural Law. >Fortunately, DEC realized that their design was crap and added a >hardware instruction to put 16-bit binary integers into big-endian >order; it had the assembler mnemonic SWAB (SWAp Bytes). The company I >worked for in the 1970s exchanged data between many PDP-11s and a >central IBM 370, usually without problems. > EBCDIC? Well, not if your data were entirely numeric. Hexadecimal floating point? >> For those who remain unaware on a Friday: >> https://en.wikipedia.org/wiki/Lilliput_and_Blefuscu#History_and_politics -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
