3 ms·

Having basic experience in any assembly language makes pointers far more clear. "Addressing modes," where a register and some constant are used to calculate th

by chasil 4y ago

Having basic experience in any assembly language makes pointers far more clear. "Addressing modes," where a register and some constant are used to calculate the source or target of a memory operation, make the equivalence of a[b]==*(a+b) much more obvious. I also wonder about the author's claims that a char is almost always 8 bits. The first SMP machine that ran Research UNIX was a 36-bit UNIVAC. I think it was ASCII, but the OS2200/EXEC8 SMP matured in 1964, so this was an old architecture at the time of the port. "Any configuration supplied by Sperry, including multiprocessor ones, can run the UNIX system." https://www.bell-labs.com/usr/dmr/www/otherports/newp.pdf https://www.bell-labs.com/usr/dmr/www/otherports/newp.pdf

jjav 4y ago
> Having basic experience in any assembly language makes pointers far more clear. That's a key point. I came to C after several years of programming in assembly and a pointer was an obvious thing. But I can see that for someone coming to C from higher level languages it might be an odd thing.
kjs3 4y ago
There was an "official" C compiler for NOS running on the CDC Cyber. As I recall, 18-bit address, 60-bit words, more than one definition of a 'char' (12-bit or 5-bit, I think). It was interesting. There were a lot of strange architectures with a C compiler. I would also point out architectures like the 8051 and 8086 made (make...they are still around) pointer arithmetic interesting.
krylon 4y ago
The C standard, as I recall defines a byte effectively as at least 8 bits. I've read that some DSP platforms use a byte (and thus a char) that is 24 bits wide, because that's what audio samples use, but supposedly those platforms rarely, if ever, handle any actual text. The standard library contains a macro CHAR_BITS that tells you I think I remember reading about a C compiler for the PDP-10 (or Lisp Machine?), also a 36-bit machine, that used a 9 bit byte. There even exists a semi-jocular RFC for UTF-9 and UTF-18.

by chasil 4y ago

jjav 4y ago

> Having basic experience in any assembly language makes pointers far more clear. That's a key point. I came to C after several years of programming in assembly and a pointer was an obvious thing. But I can see that for someone coming to C from higher level languages it might be an odd thing.

kjs3 4y ago

There was an "official" C compiler for NOS running on the CDC Cyber. As I recall, 18-bit address, 60-bit words, more than one definition of a 'char' (12-bit or 5-bit, I think). It was interesting. There were a lot of strange architectures with a C compiler. I would also point out architectures like the 8051 and 8086 made (make...they are still around) pointer arithmetic interesting.

krylon 4y ago

The C standard, as I recall defines a byte effectively as at least 8 bits. I've read that some DSP platforms use a byte (and thus a char) that is 24 bits wide, because that's what audio samples use, but supposedly those platforms rarely, if ever, handle any actual text. The standard library contains a macro CHAR_BITS that tells you I think I remember reading about a C compiler for the PDP-10 (or Lisp Machine?), also a 36-bit machine, that used a 9 bit byte. There even exists a semi-jocular RFC for UTF-9 and UTF-18.