List of platforms supported by the C standard

Question

Does anyone know of any platforms supported by the C standard, for which there is still active development work, but which are:

• not 2\'s complement or

Answer 1

I recently worked at a company which still used a version of the PDP-10, and a port of GCC to that platform. The 10 we used had a few of the attributes you list:

• Integers are not 32 or 64 bits they are 36 bits wide.
• Padding bits are used for some representations. For extended precision integers (e.g. of long long type), the underlying representation was 72-bits in which each of the 36-bit words had a sign-bit.

In addition to the above unusual attributes, there was the issue that the machine had several different byte addressing mechanisms. Bytes with widths in the range of 6-12 bits wide could be addressed by using special bits in the address itself which indicated which width and word alignment was being used. To represent a char* one could use a representation which would address 8-bit bytes, all of which were left-aligned in the word, leaving 4-bits in each 36-bit word which were not addressed at all. Alternatively 9-bit bytes could be used which would fit evenly into the 36-bit word. Both such approaches had there pitfalls for portability, but at the time I left it was deemed more practical to use the 8-bit bytes because of interaction with TCP/IP networking and standard devices which often think in terms of 16, 24, or 32-bit fields which also have an underlying structure of 8-bit bytes.

As far as I know this platform is still being used in products in the field, and there is a compiler developer at this company keeping relatively recent versions of GCC up to date in order to allow for further C development on this platform.