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class MathCaptcha extends SimpleCaptcha {
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/** Validate a captcha response */
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function keyMatch( $answer, $info ) {
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return (int)$answer == (int)$info['answer'];
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function addCaptchaAPI(&$resultArr) {
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list( $sum, $answer ) = $this->pickSum();
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$index = $this->storeCaptcha( array('answer' => $answer ) );
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$resultArr['captcha']['type'] = 'math';
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$resultArr['captcha']['mime'] = 'text/tex';
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$resultArr['captcha']['id'] = $index;
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$resultArr['captcha']['question'] = $sum;
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/** Produce a nice little form */
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list( $sum, $answer ) = $this->pickSum();
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$index = $this->storeCaptcha( array( 'answer' => $answer ) );
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$form = '<table><tr><td>' . $this->fetchMath( $sum ) . '</td>';
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$form .= '<td>' . Xml::input( 'wpCaptchaWord', false, false, array( 'tabindex' => '1' ) ) . '</td></tr></table>';
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$form .= Xml::hidden( 'wpCaptchaId', $index );
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/** Pick a random sum */
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$a = mt_rand( 0, 100 );
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$b = mt_rand( 0, 10 );
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$op = mt_rand( 0, 1 ) ? '+' : '-';
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$sum = "{$a} {$op} {$b} = ";
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$ans = $op == '+' ? ( $a + $b ) : ( $a - $b );
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return array( $sum, $ans );
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function fetchMath( $sum ) {
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$math = new MathRenderer( $sum );
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$math->setOutputMode( MW_MATH_PNG );
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$html = $math->render();
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return preg_replace( '/alt=".*?"/', '', $html );