Do Any Modern Architectures Still Exhibit 'Exotic' Properties Requiring Implementation-Defined Behavior in C and C Standards?

Exotic Architectures in the Standards Committees' Eyes

The C and C language standards wisely leave certain implementation-defined aspects open to avoid inefficient code on architectures with distinct characteristics. This raises the question of whether any modern architectures still exhibit such exotic properties.

Surprisingly, the answer is yes. The Unisys ClearPath Dorado Servers, designed for backward compatibility, retain several unique features:

• 36-bit words
• CHAR_BIT of 9
• One's complement signed representation
• 72-bit non-IEEE floating point
• Separate code and data address spaces
• Word-addressed with no dedicated stack pointer

These features highlight the importance of leaving certain language aspects undefined. By doing so, standard-conforming compilers for exotic architectures can be created without relying on emulation, ensuring efficient machine code generation.

While it is unlikely that C compilers exist for the Dorado Servers, the existence of these unique architectures underscores the wisdom of the standards committees in leaving certain low-level details implementation-defined. It empowers programmers to write portable code that can be adapted to diverse architectures without compromising efficiency.

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