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Great post.Thank you for posting the great content……I found it quiet interesting, hopefully you will keep posting such blogs... The way you have stated everything above is quite awesome. This article creates a new hope and inspiration with in me. These information really worth saying, i think you are master of the content and thank you so much sharing that valuable information. Then, we would have more positives so that there is always one for any negative :) Your statement that there is no positive for Integer.MIN_VALUE is based on a common belief that: the range of integers that can be represented in 32 bits is -2,147,483,648 to 2,147,483,647.Īctually, those who design the language could interpret the sign conversely. I think the effort has passed, we have to thank you:)) Hello, please check out six pack ab and also six pack ab nowĪ very nice page. Your stats can't be right: 7 times in eclipse-SDK-3.2-solaris-gtk 6 times in jboss-4.0.2 6 times in eclipse-SDK-3.2-solaris-gtk Did you mean to have a difference between the 1st and 3rd packages names? > Object x = bucket i would suggest the following "fix" Object x = bucket Įxcept that it would bill the '0' bucket twice as much as other buckets. So I wouldn't say it is broken just dangerous. And making Math.abs(Integer.MIN_VALUE) throw exception wouldn't really improve the situation. There isn't any value that could be returned for Math.abs(Integer.MIN_VALUE) that would be correct. So, back to my original question: Is Math.abs broken? I'm not sure how it could be any different. * of an automated search over the entire four-dimensional search space. * The shift distances in this function were chosen as the result * This is critical because HashMap uses power-of two length * hash function," which defends against poor quality hash functions. * the object's own hashCode, this method applies a "supplemental * Returns a hash value for the specified object. Sun's HashMap using the following method to stir the bits of a hashCode to try to ensure a more uniformly distributed hash value: One quick word of warning: you might not want to assume that the hashCode function gives uniformly distributed values. If you know that the length of the array is a power of two, you can also use: The (quick) recommended way to fix this simply use a integer bitwise and to clear the high bit, ensuring that the result is non-negative.
An error that comes up once out of 4 billion will be almost impossible to reproduce or find through testing.įindBugs 1.1 searches for this bug pattern. An error that occurs half the time is a lot easier to find via testing. I'm not sure whether to be relieved or worried that this problem would occur only about one time out of 4 billion.
The same pattern/problem comes up when using random 32 bit signed integers rather than hashCodes.
if the hashCode is Integer.MIN_VALUE, then the result of the Math.abs will be negative and we will likely get a negative remainder and in array index out of bounds exception. So people will call Math.abs to obtain a non-negative dividend.īut as we've discussed, Math.abs doesn't guarantee a non-negative dividend. Then roughly half the time, the remainder would be negative and we'd get an array index out of bound exception. As a result, a remainder computation can give a negative result if the dividend is negative (e.g., (-3)%2 = -1). Java defines integer division the same way. Why is the call to Math.abs there? Because essentially all processors implement integer division as rounding towards zero, rather than towards negative infinity (as most mathmeticians and computer scientists would prefer).
How can this bite you? It is not uncommon to see code such as The problem is that Integer.MIN_VALUE is -2147483648, and +2147483648 cannot be represented as a 32-bit signed integer (Integer.MAX_VALUE = 2147483647). In fact, Math.abs(Integer.MIN_VALUE) = Integer.MIN_VALUE. You'd think that Math.abs would return a non-negative integer.