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Constant Folding Expressions with constant operands can be evaluated at compile time, thus improving run-time performance and reducing code size by avoiding evaluation at compile-time. Example: In the code fragment below, the expression (3 + 5) can be evaluated at compile time and replaced with the constant 8. int f (void) { return 3 + 5; } Below is the code fragment after constant folding. int f (void) { return 8; } Notes: Constant folding is a relatively easy optimization. Programmers generally do not write expressions such as (3 + 5) directly, but these expressions are relatively common after macro expansion and other optimizations such as constant propagation. All C compilers can fold integer constant expressions that are present after macro expansion (ANSI C requirement). Most C compilers can fold integer constant expressions that are introduced after other optimizations. Some environments support several floating-point rounding modes that can be changed dynamically at run time. In these environments, expressions such as (1.0 / 3.0) must be evaluated at run-time if the rounding mode is not known at compile time. © 1990-2012 Nullstone Corporation. All Rights Reserved.