__BUILTIN_CONSTANT_P(3)

👑 NAME — __builtin_constant_p(3) 👑

okay so hey bestie 💖, you're in the Library Functions Manual, and the queen of this page is __builtin_constant_p — a GNU extension to determine compile time constants ✨. That's literally the whole vibe.

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🦋 SYNOPSIS 🦋

int
__builtin_constant_p(value);

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💅 DESCRIPTION 💅

Okay so __builtin_constant_p() is a GNU extension for determining whether a value is known to be constant at compile time 🧚. It's closely related to the concept of “constant folding” used by modern optimizing compilers ✨.

If the value is known to be a compile-time constant, a value 1 is returned 🔥. If __builtin_constant_p() returns 0, the value is not a compile-time constant in the sense that gcc(1) was unable to determine whether the value is constant or not 😭. Periodt.

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🌸 EXAMPLES 🌸

A typical example of the use of __builtin_constant_p() involves a situation where it may be desirable to fold the computation if it involves a constant, but a function call is needed otherwise 🫶. For instance, bswap16(3) is defined in NetBSD as:

#define bswap16(x) \
        (__builtin_constant_p((x)) ? \
         __byte_swap_u16_constant(x) : __BYTE_SWAP_U16_VARIABLE(x))

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👀 SEE ALSO 👀

• gcc(1)
• __builtin_object_size(3)
• __builtin_return_address(3)

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⚠️ CAVEATS ⚠️

bestie, this is a non-standard, compiler-specific extension 💀. That's the caveat, no cap.

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source: Debian 💋 — this page is dated December 19, 2010 🎀. stay iconic, bestie 💖