Binary Search Algorithm

Over the weekend I read some chapters of Beautiful Code book. It is really interesting and I am seeing the beauty in programming :). I read the Beautiful Test chapter and impressed with the example it has introduced. It is Binary Search algorithm. It says that this algorithm was published in 1946 but took 12 years for the first binary search without bugs to be published. It is amazing!!!
You can refer the most common bug here.

Further it shows that the algorithm may not returns the first position of the target value. But for the binary search algorithm, only pre-condition is to have a sorted array[1]. A sorted array can have duplicate values. If so algorithm should return the first position, as I guess. But the algorithm published in most sites(in wikipedia too) do not consider this point.
Here is the changed algorithm to handle duplicate values,

public static int binarySearch(int[] array, int target){
int low = 0;
int high = array.length - 1;
while(low <= high){
int mid = calculateMidPoint(low, high);
int midValue = array[mid];

if(midValue < target)
low = mid + 1;
else if(midValue > target)
high = mid -1;
else{
while(mid!=0 && target == array[mid-1]) //loop backward to check whether duplicate values present
mid -= 1;
return mid;
}
}
return -1;
}

Here is my java implementation of this algorithm and test classes. My reference is Beautiful Code book.

[1] http://en.wikipedia.org/wiki/Binary_search