Redundant Code - Examples

Examples

int foo(int iX) { int iY = iX*2; return iX*2; }

The second iX*2 expression is redundant code and can be replaced by a reference to the variable iY. Alternatively, the definition int iY = iX*2 can instead be removed.

Consider:

#define min(A,B) ((A)<(B)?(A):(B)) int shorter_magnitude(int u1, int v1, int u2, int v2) { /* Returns the shorter magnitude of (u1,v1) and (u2,v2) */ return sqrt(min(u1*u1 + v1*v1, u2*u2 + v2*v2)); }

As a consequence of using the C preprocessor, the compiler will only witness the expanded form:

int shorter_magnitude(int u1, int v1, int u2, int v2) { int temp; if (u1*u1 + v1*v1 < u2*u2 + v2*v2) temp = u1*u1 + v1*v1; /* Redundant */ else temp = u2*u2 + v2*v2; /* Redundant */ return sqrt(temp); }

Because the use of min/max macros is very common, modern compilers are trained to recognize and eliminate redundancy caused by their use.

There is no redundancy, however, in the following code:

#define max(A,B) ((A)>(B)?(A):(B)) int random(int cutoff, int range) { /* Returns (cutoff, cutoff, cutoff, ..., cutoff+1, cutoff+2, ... range) */ return max(cutoff, rand%range); }

The reason is that its implementation is incorrect. If the initial call to rand, modulo range, is less than or equal to cutoff, rand will be called a second time for a second computation of rand%range, which may result in a value that is actually lower than the cutoff. The max macro will thus not work for this function.