c++ - Exotic architectures the standards committees care about

Question

I know that the C and C++ standards leave many aspects of the language implementation-defined just because if there is an architecture with other characteristics, it would be very difficult or impossible to write a standard conforming compiler for it.

I know that 40 years ago any computer had its own unique specification. However, I don't know of any architectures used today where:

• CHAR_BIT != 8
• signed is not two's complement (I heard Java had problems with this one).
• Floating point is not IEEE 754 compliant (Edit: I meant "not in IEEE 754 binary encoding").

The reason I'm asking is that I often explain to people that it's good that C++ doesn't mandate any other low-level aspects like fixed sized types^?. It's good because unlike 'other languages' it makes your code portable when used correctly (Edit: because it can be ported to more architectures without requiring emulation of low-level aspects of the machine, like e.g. two's complement arithmetic on sign+magnitude architecture). But I feel bad that I cannot point to any specific architecture myself.

So the question is: what architectures exhibit the above properties?

? uint*_ts are optional.

Answer 1

Take a look at this one

Unisys ClearPath Dorado Servers

offering backward compatibility for people who have not yet migrated all their Univac software.

Key points:

• 36-bit words
• CHAR_BIT == 9
• one's complement
• 72-bit non-IEEE floating point
• separate address space for code and data
• word-addressed
• no dedicated stack pointer

Don't know if they offer a C++ compiler though, but they could.

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And now a link to a recent edition of their C manual has surfaced:

Unisys C Compiler Programming Reference Manual

Section 4.5 has a table of data types with 9, 18, 36, and 72 bits.