Safer Code – Secure Coding In C \ C++ And More..

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One of the ways to optimize your code for speed is to unroll the loops you have in your program. If you don’t know what loop unrolling is, then see the following simple example, where we are trying to copy a 5 element long string:
A Simple Loop:

for (i = 0 ; i < 5; ++i)
{
    *j++ = *k++;
}

The same loop unrolled:

*j++ = *k++;
*j++ = *k++;
*j++ = *k++;
*j++ = *k++;
*j++ = *k++;

Now, the unrolled version is definitely going to be faster because of the following reasons:

1. There are no branches any more. In a loop, the compiler has to insert branches to jump back to the for statement.

2. There are no condition checks. In a loop, the value of i is checked every time to see what to do next.

3. A third rather hidden, but really important, advantage is that unrolled code can be pipelined efficiently by the processor hence resulting in faster execution.

The above code in itself might not show you any perceivable difference in execution time, but it does become crucial when the loops are of much higher magnitude and especially in embedded/real time scenarios.

Now, the loop unrolling can be done by the compiler or manually by the coder. In this part, we will see how to facilitate compiler to carry out loop unrolling efficiently. (more...)

© Safer Code | Tweak Your Code For Speed: Unroll Those Loops Part 1

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Except for few good C programmers, others generally tend to ignore variable initialization or I should rather say “proper variable initialization”. Generally seen, the variable declaration itself is not done with a good thinking. Improper local variable initialization might not be good for the working of the program but improper global variable initialization might get your software or system hacked.

The uninitialized variable or a wrongly initialized variable might lead a program to change its normal course of flow from the intended one. For example: If a variable “index” is being used for array navigation and is left uninitialized, it might contain a garbage value which can lead to array index out of bounds error. or if the variable “index” is initialized wrongly to –1, it might lead to serious flaw in code flow. Even if an integer value is being initialized to ‘0’, it might lead to a security check bypass because for some programs, even a ‘0’ is considered a valid value.

Lets take an example of a code piece.

 int isMachineRunning = GetMachineStatus();
 int state = GetUserState(isMachineRunning);
 int userid = 0;
 if (state) {
	userid = ExtractUserID(state);
 }
/* do stuff */
if (uid == 0) {
	DoAdminThings();
}

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© Safer Code | Improper Variable Initialization

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