Why Do C and C Convert Shorts to Ints for Arithmetic Operations?

Why Convert Shorts to Ints Before Arithmetic Operations in C and C ?

In C and C , arithmetic operations involving short data types require conversion to int due to historical origins and performance considerations.

Historical Rationale

As per the C Rational Document (section 6.3.1.8), the requirement for explicit conversion was introduced to allow wider calculations, resulting in more efficient code and improved accuracy. This approach also allowed for the use of narrower types while preserving results.

Type Promotion

When performing arithmetic operations, integer promotions are applied to short operands. If int can represent all values of short, conversion to int occurs. Otherwise, the value is promoted to unsigned int.

Unsigned Preserving vs. Value Preserving

Historically, implementations differed in their approach to promoting unsigned types. Unsigned preserving promoted all types to unsigned int, while value preserving promoted short to signed int if applicable, and unsigned short to unsigned int otherwise.

Performance Advantages

Converting to a wider type like int allows operations to be performed more efficiently, as broader registers can be utilized. By promoting short to int, the potential for overflows and data loss is reduced, especially when performing calculations with a large number of short values.

Conclusion

The conversion of short to int before arithmetic operations in C and C stems from historical reasons and performance benefits. It ensures consistency in calculations, improves code efficiency, and minimizes the risk of errors.

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