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Sum a Signed Array

This function sums an array of signed dwords.

The program returns a dword as the final value, but allows the intermediate result to be larger than a dword can hold. It tracks the “result,” which is the dword total of the elements in the array, as well as an overflow/underflow “counter.” Each time the cumulative sum of the elements overflows (meaning it is more than 2³¹-1, the highest value a signed dword can hold), the counter is incremented; each time the cumulative sum underflows (meaning it is less than -2³¹, the lowest value a signed dword can hold), the counter is decremented. The net effect is that the counter functions ...