Description:
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Solr expects boosts to be specified as a float with a dot as decimal character.

In solr_functions_document.c, document_boost and field_boost is converted to a string with sprintf. sprintf uses locale info for converting float into a string.

In an environment where decimal delimiter is a comma, solr will not accept the documents.

One solution might be to temporarily switch locale to C before the sprintf calls. Another one would not to use sprintf and use another function that is not locale aware.

Test script:
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<?php
/* use a system locale where decimal delimiter is not a dot. */
$clientOptions = array('hostname' => 'localhost', 'port' => '8080', 'path' => '/solr/core');
$solrClient = new \SolrClient($clientOptions);
$document = new \SolrInputDocument();
document->setBoost(1.0);
$solrClient->addDocuments(array($document));
?>

Expected result:
----------------
Solr would accept inserted documents not depending of the locale settings.

Actual result:
--------------
Solr fails importing the document with java.lang.NumberFormatException: For input string: "1,0"