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POPacking many bounded integers into a large single integer
 

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  1. POPacking many bounded integers into a large single integer
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    <p>I have to store millions of entries in a database. Each entry is identified by a set of unique integer identifiers. For example a value may be identified by a set of 10 integer identifiers, each of which are less than 100 million.</p> <p>In order to reduce the size of the database, I thought of the following encoding using a single 32 bit integer value.</p> <pre> Identifier 1: 0 - 100,000,000 Identifier 2: 100,000,001 - 200,000,000 . . . Identifier 10: 900,000,001 - 1,000,000,000 </pre> <p>I am using Java. I can write a simple method to encode/decode. The user code does not have to know that I am encoding/decoding during fetch/store.</p> <p>What I want to know is: what is the most efficient (fastest) and recommended way to implement such encoding/decoding. A simple implementation will perform a large number of multiplications/subtractions.</p> <p>Is it possible to use shifts (or bitwise operations) and choose different partition size (the size of each segment still has to be close to 100 million)?</p> <p>I am open to any suggestions, ideas, or even a totally different scheme. I want to exploit the fact that the integer identifiers are bounded to drastically reduce the storage size without noticeably compromising performance.</p> <p>Edit: I just wanted to add that I went through some of the answers posted on this forum. A common solution was to split the bits for each identifier. If I use 2 bits for each identifier for a total of 10 identifiers, then my range of identifiers gets severely limited.</p>
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    1. USSantosh Tiwari
    1. USSantosh Tiwari
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    1. COyou'd have to use powers of 2 for your ranges to get bit shifting to work.
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      1. USMeBigFatGuy
    2. COCan you gice an example of how such an encoded integer would look like (as well as how you'd decode manually)? Please use arbitrary ids (like `144,560,000`, `200,0158,945`, `399,888,777` etc.) for your example
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      1. USThomas
    3. CONote that with shifting you'd have 3 bytes per id only (if you want to put 10 ids into 32 bits). Thus each id could only have up to 8 different values.
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      1. USThomas
 

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