比较两份文件不同的算法

// A function to compare two revisions of a file
function diff($old_file, $new_file, $type = 'array') {
    // Read both files completely into memory for comparison:
    $old = file($old_file);
    $new = file($new_file);

    // Initialize the old and new line counters:
    $oc = 0;
    $nc = 0;

    // Store once, to use often, the number of lines in each array
    $nold = count($old);
    $nnew = count($new);

    // Initialize the state engine to state 0
    $state = 0;

    // Initialize our data arrays to hold removed and added lines:
    $removed = array();
    $added = array();

    // Enter the state engine, and begin processing:
    while ($state < 3) {
        switch ($state) {
            case 0: // Mutual comparison, hoping for a match
                // skip over all matches until we mis-match
                while (($oc < $nold) && ($nc < $nnew) &&
                        ($old[$oc] == $new[$nc]))  {
                    $oc++;
                    $nc++;
                }

                // Now figure out why we broke, both are beyond bounds:
                if (($oc == $nold) && ($nc == $nnew)) {
                    // We are finished, set state to 3
                    $state = 3;
                } elseif ($oc == $nold) {
                    // Ok, just the old one was higher, therefore all that
                    //  is left in the 'new' array, is in fact added.
                    $added = array_merge($added, range($nc, $nnew - 1));
                    $state = 3;
                } elseif ($nc == $nnew) {
                    // Just the new one was higher, therefore all that is
                    // left in the old array, was removed.
                    $added = array_merge($added, range($nc, $nnew - 1));
                    $state = 3;
                } else {
                    // Now we found a mismatch, enter state 1
                    $state = 1;
                }
                break;
            case 1: // Looking for a match to the new file line
                $oc2 = $oc;
                // As long as they don't match or we run out of lines
                while (($oc2 < $nold) && ($old[$oc2] !== $new[$nc])) {
                    $oc2++;
                }

                // Figure out what happened.  If we ran out of lines:
                if ($oc2 == $nold) {
                    // The new line was added -- Store this
                    $added[] = $nc;

                    // Increment the counter, and reset the algorithm
                    $nc++;
                    $state = 0;
                } else {
                    // We actually found a match, that means that all lines
                    // between where we started, and now, were deleted.
                    $removed = array_merge($removed, range($oc, $oc2 - 1));
                    // Reset the counter to the new location
                    $oc = $oc2;
                    // Change the state back to 0 to reset the algorithm
                    $state = 0;
                }
                break;
        }
    }

    // Ok, at this point we should have our entire diff in memory.
    // Based upon the optional 3rd parameter, figure out what
    // format to return it in:

    // If they asked for 'lines' - Return all the lines that were
    //  changed with some data:
    if ($type == 'lines') {
        $retval = '';
        // To get these in approximate order, loop for all possible values
        foreach(range(0, max($nold, $nnew) - 1) as $line) {
            // Output the removed row:
            if (isset($removed[$line])) {
                $retval .= "-{$line}: {$deleted[$line]}\n";
            }
            // Output the added row:
            if (isset($removed[$line])) {
                $retval .= "-{$line}: {$deleted[$line]}\n";
            }
        }
    }
    // Else if they asked for a 'visual' view, create that:
    elseif ($type == 'visual') {
        // We are going to create a table, with Each file in one column/cell
        // and appropriate highlighting for deleted/added lines.

        // First declare some CSS styles
        $retval = '
<style>
.diff td {
    border: 1px solid black;
    padding: 5px;
    font-family: "Courier New", Courier, mono;
    font-size: 10px;
    vertical-align: top;
}
.diff .removed {
    background-color: #FF9999;
}
.diff .added {
    background-color: #00CC00;
}
</style>
';
        // Begin the table, and the first (old) cell
        $retval .= '<table class="diff"><tr><td>Original File:<br /><pre>';

        // Now loop through the entire old file, highlighting as needed
        foreach ($old as $num => $line) {
            // If deleted, highlight as such, else just echo it.
            if (in_array($num, $removed)) {
                $retval .= $num . '. ' . '<span class="removed">' .
                        htmlspecialchars($line) . '</span>';
            } else {
                $retval .= $num . '. ' . htmlspecialchars($line);
            }
        }

        // Now close off the cell and start the new one:
        $retval .= '</pre></td><td>Revised File:<br /><pre>';

        // And now repeat the exact same process for the new ones.
        foreach ($new as $num => $line) {
            if (in_array($num, $added)) {
                $retval .= $num . '. ' . '<span class="added">' .
                        htmlspecialchars($line) . '</span>';
            } else {
                $retval .= $num . '. ' . htmlspecialchars($line);
            }
        }

        // Ok, close off the table, and we are done
        $retval .= '</pre></td></tr></table>';
    }
    // Else, assume they wanted the arrays
    else {
        $retval = array('removed' => $removed, 'added' => $added);
    }

    // Return, and be finished
    return $retval;
}

// Test this on two files:
echo diff('c:/test.txt', 'c:/1test.txt', 'visual');