Programming Embedded Systems in C and C++

144 Chapter 10: Optimizing Your Code

lines of the high-level language program might have been removed from the pro-

gram altogether (as they were in the previous example)! As a result, you might be

unable to set a breakpoint on a particular line of the program or examine the

value of a variable of interest.

Once you’ve got the automatic optimizations working, here are some tips for fur-

ther reducing the size of your code by hand:

Avoid standard library routines

One of the best things you can do to reduce the size of your program is to

avoid using large standard library routines. Many of the largest are expensive

only because they try to handle all possible cases. It might be possible to

implement a subset of the functionality yourself with significantly less code.

For example, the standard C library’s sprintf routine is notoriously large. Much

of this bulk is located within the floating-point manipulation routines on

which it depends. But if you don’t need to format and display floating-point

values (%f or %g), you could write your own integer-only version of sprintf

and save several kilobytes of code space. In fact, a few implementations of the

standard C library (Cygnus’ newlib comes to mind) include just such a func-

tion, called siprintf.

Native word size

Every processor has a native word size, and the ANSI C and C++ standards

state that data type int must always map to that size. Manipulation ...