The Google SparseHash project contains several C++ template hash-map implementations with different performance characteristics, including an implementation that optimizes for space and one that optimizes for speed.

Coccinelle is a program matching and transformation engine which
provides the language SmPL (Semantic Patch Language) for specifying
desired matches and transformations in C code. Coccinelle was
initially targeted towards performing collateral evolutions in Linux.
Such evolutions comprise the changes that are needed in client code
in response to evolutions in library APIs, and may include
modifications such as renaming a function, adding a function argument
whose value is somehow context-dependent, and reorganizing a data
structure. Beyond collateral evolutions, Coccinelle is successfully
used (by us and others) for finding and fixing bugs in systems code.