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(PHP 5 >= 5.1.2, PECL hash >= 1.1)
hash_update — Fügt Daten an einen aktiven Hash-Kontext an
Hashing-Kontext, zurückgegeben von hash_init().
Nachricht, die in den Hash-Kontext eingefügt wird.
Returns TRUE.
A simple example on incremental file hashing:
$fp = fopen($file, "r");
$ctx = hash_init('sha256');
while (!feof($fp)) {
$buffer = fgets($fp, 65536);
hash_update($ctx, $buffer);
}
$hash = hash_final($ctx, true);
fclose($fp);
While incremental hashing is quite slow, it's the easiest way to hash
- parts of large files: I.e., a 700MB avi video uses first x bytes to store metadata, so in order to hash the avi's data only, you have to fseek to data start and use incremental hashing
- streaming data if php just proxies the data
- whenever it's inadequate or impossible to store the data being hashed into memory (i.e. because of their size) or on disc.
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