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copied!<p>This algorithm is smart and would indeed minimize write operations. So the length value will converge to a balance between shortest length and <strong>absence</strong> of collisions. </p> <p>You can relax the constrain of absence of collision by using strategies used in hash tables. Try some other unique IDs before falling back to incrementing the length. </p> <p>I would thus suggest you add a test counter to the end of the hashed string initialized to 0. If the generated ID is already used, increment the counter and retry until a maximum counter value is reached after what you increase the length.</p> <p>You will end up with a more efficient use of your ID address space and much less frequent length increments. </p> <p>Regarding your question about the length limit of MD5 I think the choice of MD5 is an overkill. You don't really need a cryptographic (pseudo)secure hash. What you need is a random bit generator for which you can use crc32 (or adler which is faster). Especially if the code is to be run on a mobile phone. To implement a random bit generator with crc32, prepend a 32bits value to the string to hash and initialize it with a constant value of your choice (the seed). Then compute the crc32 on this string. If you need more bytes, write the obtained crc32 value in the 32bits in front of the string and recompute the crc32. Iterate until you have enough bits. You may replace the crc32 with the algorithm of your choice. This yields a cheap and fast random bit generator where the initial constant is the seed. </p> <p>With this algorithm you minimize the number of random bits generated and also have no upper limit in length. </p> <p>Regarding encoding, you didn't specify the constrains. Can you use upper and lower case letters with the digits ? Your example uses an alphabet of 36 different ASCII values. Once you have the pseudo random number generator described above that can generate as many bytes as desired, simply define length to be the number of letters of your ID and pick the next letter with a modulo of the next random byte. You'll know then exactly how many bytes to generate in one go and generating the ID is trivial.</p>

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