Why Do C and C Promote `short` to `int` During Arithmetic Operations?

Why Convert Short to Int for Arithmetic Operations in C and C ?

C and C require converting short to int before performing arithmetic operations. This requirement stems from historical design decisions that accommodated varying hardware architectures and performance optimizations.

Background on Integer Promotions

In C, integer promotions were introduced to determine how data types were automatically converted in expressions. The usual arithmetic conversions applied to arithmetic expressions involve promoting short to int if it can represent all values of short. Otherwise, it is promoted to unsigned int.

Rationale for Wider Calculations

According to the C standard rationale, allowing calculations in wider types than necessary was introduced to:

• Generate smaller and faster code
• Provide more accurate results

This design decision is attributed to the varying hardware architectures at the time, where using wider types could result in more efficient code execution.

Implications for Short Operands

When a short operand is encountered in an arithmetic operation, it undergoes integer promotions. This promotion typically converts it to int, which provides a wider range of values and ensures consistent data types for operations.

Example

Consider the following code snippet:

short s = 1, t = 2;
auto x = s + t;

Here, s and t are short types. However, the result of their addition is stored in x, which will have type int. This aligns with the usual arithmetic conversions and integer promotions defined in the C standard.

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