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up vote 0 down vote favorite

The goal is to store the hash on a mysql database, using INT (not BIGINT or MEDIUMINT). md5('string', true) returns binary data, 16 bytes of hash. I thought i could grep the first 4 bytes and convert it to an INT(32bit/4bytes) integer, but i don't know how to do it.

What do you suggest? Thanks.

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$int = bindec(substr(md5('string', true),0,4)) or $int = hexdec(substr(md5('string'),0,8)) - but, fairly obviously, this does not store the whole hash, only the first 4 bytes of it. –  DaveRandom Dec 15 '11 at 13:42
    
May I ask, what is going to be such a "hash" purpose? –  Your Common Sense Dec 15 '11 at 13:50
    
@DaveRandom: bindec won't work (hexdec does). –  hakre Dec 15 '11 at 13:54
    
@hakre indeed it does not work - why is that? –  DaveRandom Dec 15 '11 at 13:56
    
@cedivad: Is the INT in your MySQL signed or unsigned? –  hakre Dec 15 '11 at 13:56
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3 Answers

up vote 6 down vote

You are looking for PHP function crc32().

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That's more a comment than an answer. –  hakre Dec 15 '11 at 14:00
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up vote 2 down vote

Use crc32, it will return a 32bit int.

var_dump (crc32 ("hello world"));
var_dump (crc32 ("world hello"));

output

int(222957957)
int(1292159901)

PHP: crc32 - Manual

Generates the cyclic redundancy checksum polynomial of 32-bit lengths of the str. This is usually used to validate the integrity of data being transmitted.

Because PHP's integer type is signed, and many crc32 checksums will result in negative integers, you need to use the "%u" formatter of sprintf() or printf() to get the string representation of the unsigned crc32 checksum.

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up vote 2 down vote 
ord($hash[0]) * 16777216 + ord($hash[1]) * 65536 + ord($hash[2]) * 256 + ord($hash[3]) ;

Or:

unpack("L", substr($hash,0,4));

But Frosty Z's solution is better.

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