An implementation of a page signature. It calculates an MD5 hash of a plain text "profile" of a page. The algorithm to calculate a page "profile" takes the plain text version of a page and performs the following steps:

• remove all characters except letters and digits, and bring all characters to lower case,
• split the text into tokens (all consecutive non-whitespace characters),
• discard tokens equal or shorter than MIN_TOKEN_LEN (default 2 characters),
• sort the list of tokens by decreasing frequency,
• round down the counts of tokens to the nearest multiple of QUANT (QUANT = QUANT_RATE * maxFreq, where QUANT_RATE is 0.01f by default, and maxFreq is the maximum token frequency). If maxFreq is higher than 1, then QUANT is always higher than 2 (which means that tokens with frequency 1 are always discarded).
• tokens, which frequency after quantization falls below QUANT, are discarded.
• create a list of tokens and their quantized frequency, separated by spaces, in the order of decreasing frequency.

This list is then submitted to an MD5 hash calculation.

echo "The Rocky Horror Picture Show premiered in London, the first in its record-breaking run in cinemas, which continues in limited release." | go run textprofile.go

592325199d7e02121eaf3304d10cc681