From 1430406399618877486 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,738ae3371beb3408 X-Google-Attributes: gidf78e5,public From: Ron Natalie Subject: Re: portable method of determining endianness byte order. Date: 1999/12/07 Message-ID: <384D2A84.5C743996@sensor.com>#1/1 X-Deja-AN: 557760543 Content-Transfer-Encoding: 7bit Approved: Fergus Henderson References: <38329967.470B6CED@hqs.mid.gmeds.com> <38359FF5.AB0B77E9@zetec.com> <3846CA71.5792390E@tribble.com> X-Original-Date: Tue, 07 Dec 1999 10:40:52 -0500 X-Accept-Language: en Content-Type: text/plain; charset=x-user-defined X-Complaints-To: news@news.unimelb.edu.au X-Trace: ariel.ucs.unimelb.edu.au 944585077 26762 128.250.37.153 (7 Dec 1999 16:44:37 GMT) Organization: Sensor Systems X-Auth: PGPMoose V1.1 PGP comp.std.c++ iQBFAgUAOE05h+EDnX0m9pzZAQE3dQF/bwX+WcRUofLhQxnrBo3JKSKuV2X5J8RL YLnHOqUxVsSXlgrjUIZBY/lUqgN8kZ9a =js9T Mime-Version: 1.0 NNTP-Posting-Date: 7 Dec 1999 16:44:37 GMT Newsgroups: comp.std.c++ Hyman Rosen wrote: > > David R Tribble writes: > > No, you're thinking of its predecessor, the PDP-11. > > VAX integers (32 bits) were little-endian (e.g., 0x11223344 was > > <0x44,0x33,0x22,0x11>), while PDP-11 long ints (32 bits) were > > mixed-endian (e.g., 0x11223344 was <0x22,0x11,0x44,0x33>). > > Sounds right. When I first started programming in C, it was on a > PDP-11/45, using a compiler which didn't implement longs or unions, > and which represented structure fields as absolute offsets, so that > no two structures could have the same field names unless the fields > were at the same offset in each structure. That was around 1979. > Ah yes, those were the days. That's why most system code from UNIX uses structure members with the type uniquer (u_uid) at the beginning as the tags needed to be unique. I still remember the following construct in the kernel: #define PS 0177776 struct { int integ; } if(PS->integ) ... The problem is that the PDP-11 didn't really support 32 bit math. The implementation put the high order word of a long into the second place word in memory because that way it would be compatibile with 16 bit values when sloppily mixed. -Ron p&P6 --- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@ncar.ucar.edu ] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://reality.sgi.com/austern_mti/std-c++/faq.html ]