Type Punning

Definitions

1. Reinterpreting the raw bit pattern of a value as a different type without performing any conversion — for example, reading an IEEE 754 float's bits as an integer via a union or `memcpy` in C. This is useful for bit-level tricks (like the fast inverse square root hack) but violates strict aliasing rules if done via pointer casts, potentially invoking undefined behavior.

   In plain English: A low-level trick where you look at the raw bits of one type of data and pretend they represent a completely different type.

   Example: "The fast inverse square root in Quake III uses type punning through a pointer cast to read a float's bits as an int — technically undefined behavior, but it worked on every compiler of the era."

Related Terms

• DMA
• Pointer
• Page Cache
• Static Variable
• Thread Local
• Transactional Memory
• Translation Unit
• Undefined Behavior