diff --git a/system/core/Input.php b/system/core/Input.php
index adc5f7a..4d73fa4 100644
--- a/system/core/Input.php
+++ b/system/core/Input.php
@@ -768,9 +768,9 @@
 
 			foreach ($_SERVER as $key => $val)
 			{
-				if (strpos($key, 'HTTP_') === 0)
+				if (sscanf($key, 'HTTP_%s', $header) === 1)
 				{
-					$headers[substr($key, 5)] = $this->_fetch_from_array($_SERVER, $key, $xss_clean);
+					$headers[$header] = $this->_fetch_from_array($_SERVER, $key, $xss_clean);
 				}
 			}
 		}
diff --git a/system/core/Output.php b/system/core/Output.php
index 9300df3..6312ccd 100644
--- a/system/core/Output.php
+++ b/system/core/Output.php
@@ -256,9 +256,9 @@
 	{
 		for ($i = 0, $c = count($this->headers); $i < $c; $i++)
 		{
-			if (preg_match('/^Content-Type:\s(.+)$/', $this->headers[$i][0], $matches))
+			if (sscanf($this->headers[$i][0], 'Content-Type: %s', $content_type) === 1)
 			{
-				return $matches[1];
+				return $content_type;
 			}
 		}
 
diff --git a/system/helpers/date_helper.php b/system/helpers/date_helper.php
index 0fa400d..7a0552b 100644
--- a/system/helpers/date_helper.php
+++ b/system/helpers/date_helper.php
@@ -677,8 +677,8 @@
 		$is_unix = ! ( ! $is_unix OR $is_unix === 'days');
 
 		// Validate input and try strtotime() on invalid timestamps/intervals, just in case
-		if ( ( ! preg_match('/^[0-9]+$/', $unix_start) && ($unix_start = @strtotime($unix_time)) === FALSE)
-			OR ( ! preg_match('/^[0-9]+$/', $mixed) && ($is_unix === FALSE OR ($mixed = @strtotime($mixed)) === FALSE))
+		if ( ( ! ctype_digit((string) $unix_start) && ($unix_start = @strtotime($unix_time)) === FALSE)
+			OR ( ! ctype_digit((string) $mixed) && ($is_unix === FALSE OR ($mixed = @strtotime($mixed)) === FALSE))
 			OR ($is_unix === TRUE && $mixed < $unix_start))
 		{
 			return FALSE;
diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index d23be1a..92ccde6 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -1935,7 +1935,7 @@
 
 		$this->_debug_msg[] = '<pre>'.$cmd.': '.$reply.'</pre>';
 
-		if ( (int) substr($reply, 0, 3) !== $resp)
+		if ((int) substr($reply, 0, 3) !== $resp)
 		{
 			$this->_set_error_message('lang:email_smtp_error', $reply);
 			return FALSE;
@@ -2093,7 +2093,7 @@
 		$CI =& get_instance();
 		$CI->lang->load('email');
 
-		if (substr($msg, 0, 5) !== 'lang:' OR FALSE === ($line = $CI->lang->line(substr($msg, 5))))
+		if (sscanf($msg, 'lang:%s', $line) !== 1 OR FALSE === ($line = $CI->lang->line($line)))
 		{
 			$this->_debug_msg[] = str_replace('%s', $val, $msg).'<br />';
 		}
diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index e50eee4..b0ba8bb 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -199,12 +199,10 @@
 
 		// Is the field name an array? If it is an array, we break it apart
 		// into its components so that we can fetch the corresponding POST data later
+		$indexes = array();
 		if (preg_match_all('/\[(.*?)\]/', $field, $matches))
 		{
-			// Note: Due to a bug in current() that affects some versions
-			// of PHP we can not pass function call directly into it
-			$x = explode('[', $field);
-			$indexes[] = current($x);
+			sscanf($field, '%[^[][', $indexes[0]);
 
 			for ($i = 0, $c = count($matches[0]); $i < $c; $i++)
 			{
@@ -218,7 +216,6 @@
 		}
 		else
 		{
-			$indexes	= array();
 			$is_array	= FALSE;
 		}
 
@@ -673,11 +670,7 @@
 			// Strip the parameter (if exists) from the rule
 			// Rules can contain a parameter: max_length[5]
 			$param = FALSE;
-			if (preg_match('/(.*?)\[(.*)\]/', $rule, $match))
-			{
-				$rule	= $match[1];
-				$param	= $match[2];
-			}
+			sscanf($rule, '%[^[][%[^]]', $rule, $param);
 
 			// Call the function that corresponds to the rule
 			if ($callback === TRUE)
@@ -796,11 +789,8 @@
 	{
 		// Do we need to translate the field name?
 		// We look for the prefix lang: to determine this
-		if (strpos($fieldname, 'lang:') === 0)
+		if (sscanf($fieldname, 'lang:%s', $line) === 1)
 		{
-			// Grab the variable
-			$line = substr($fieldname, 5);
-
 			// Were we able to translate the field name?  If not we use $line
 			if (FALSE === ($fieldname = $this->CI->lang->line($line)))
 			{
@@ -1002,7 +992,7 @@
 	 */
 	public function is_unique($str, $field)
 	{
-		list($table, $field) = explode('.', $field);
+		sscanf($field, '%[^.].%[^.]', $table, $field);
 		if (isset($this->CI->db))
 		{
 			$query = $this->CI->db->limit(1)->get_where($table, array($field => $str));
diff --git a/system/libraries/Image_lib.php b/system/libraries/Image_lib.php
index 9379e3e..7f937f9 100644
--- a/system/libraries/Image_lib.php
+++ b/system/libraries/Image_lib.php
@@ -605,7 +605,7 @@
 		// Set the quality
 		$this->quality = trim(str_replace('%', '', $this->quality));
 
-		if ($this->quality === '' OR $this->quality === 0 OR ! preg_match('/^[0-9]+$/', $this->quality))
+		if ($this->quality === '' OR $this->quality === 0 OR ! ctype_digit($this->quality))
 		{
 			$this->quality = 90;
 		}
@@ -1277,8 +1277,8 @@
 		if ($this->wm_use_drop_shadow === FALSE)
 			$this->wm_shadow_distance = 0;
 
-		$this->wm_vrt_alignment = strtoupper(substr($this->wm_vrt_alignment, 0, 1));
-		$this->wm_hor_alignment = strtoupper(substr($this->wm_hor_alignment, 0, 1));
+		$this->wm_vrt_alignment = strtoupper($this->wm_vrt_alignment[0]);
+		$this->wm_hor_alignment = strtoupper($this->wm_hor_alignment[0]);
 
 		// Set verticle alignment
 		if ($this->wm_vrt_alignment === 'M')
@@ -1518,13 +1518,13 @@
 	public function image_reproportion()
 	{
 		if (($this->width === 0 && $this->height === 0) OR $this->orig_width === 0 OR $this->orig_height === 0
-			OR ( ! preg_match('/^[0-9]+$/', $this->width) && ! preg_match('/^[0-9]+$/', $this->height))
-			OR ! preg_match('/^[0-9]+$/', $this->orig_width) OR ! preg_match('/^[0-9]+$/', $this->orig_height))
+			OR ( ! ctype_digit((string) $this->width) && ! ctype_digit((string) $this->height))
+			OR ! ctype_digit((string) $this->orig_width) OR ! ctype_digit((string) $this->orig_height))
 		{
 			return;
 		}
 
-		// Sanitize so we don't call preg_match() anymore
+		// Sanitize
 		$this->width = (int) $this->width;
 		$this->height = (int) $this->height;
 
diff --git a/system/libraries/Trackback.php b/system/libraries/Trackback.php
index c923a62..d303503 100644
--- a/system/libraries/Trackback.php
+++ b/system/libraries/Trackback.php
@@ -394,7 +394,7 @@
 			}
 		}
 
-		return preg_match('/^[0-9]+$/', $tb_id) ? $tb_id : FALSE;
+		return ctype_digit((string) $tb_id) ? $tb_id : FALSE;
 	}
 
 	// --------------------------------------------------------------------