Programming Embedded Systems, 2nd Edition

Decreasing Code Size

As stated earlier, when it comes to reducing code size, your best bet is to let the compiler do the work for you. However, if the resulting program is still too large for your available ROM, there are several programming techniques you can use to further reduce the size of your program.

Once you’ve got the automatic optimizations working, take a look at these tips for further 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 routines are costly in terms of size because they try to handle all possible cases. For example, the strupr function might be small, but a call to it might drag other functions such as strlower, strcmp, strcpy, and others into your program whether they are used or not.

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 (%a, %e, %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’s newlib comes to mind) include just such a function, called siprintf.

Use goto statements

As with ...