From 0a4028e9f1170bda49fe6bc10b9b1be04441d8b2 Mon Sep 17 00:00:00 2001
From: John Denker <jsd@av8n.com>
Date: Thu, 11 Nov 2021 16:02:59 -0700
Subject: implement floor(x), ceil(x), and modulo (x % y)

---
 parser.php | 122 ++++++++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 92 insertions(+), 30 deletions(-)

(limited to 'parser.php')

diff --git a/parser.php b/parser.php
index 80e01c2..cd7e6c2 100644
--- a/parser.php
+++ b/parser.php
@@ -858,6 +858,61 @@ class qtype_algebra_parser_divide extends qtype_algebra_parser_term {
     );
 }
 
+/**
+ * Class representing a modulo operation in an algebraic expression.
+ *
+ * The parser creates an instance of this term when it finds a string matching the modulo
+ * operator's syntax. The string which corresponds to the term is passed to the constructor
+ * of this subclass.
+ */
+class qtype_algebra_parser_modulo extends qtype_algebra_parser_term {
+
+    /**
+     * Constructs an instance of a modulo operator term.
+     *
+     * This function initializes an instance of a modulo operator term using the string which
+     * matches the modulo operator expression. Since this is simply the character representing
+     * the operator it is not used except when producing a string representation of the term.
+     *
+     * @param $text string matching the term's regular expression
+     */
+    public function __construct($text) {
+        parent::__construct(self::NARGS, self::$formats, $text);
+    }
+
+    /**
+     * Evaluates the modulo operation numerically.
+     *
+     * Overrides the base class method to simply return the numerical value of the modulo
+     * operation. The method evaluates the two arguments of the term and then performs
+     * the required operation to get the return value.
+     *
+     * @param $params array of values keyed by variable name
+     * @return the numerical value of the term given the provided values for the variables
+     */
+    public function evaluate($params) {
+        $this->check_arguments();
+        // Get the value we are trying to modulo by.
+        $denom = $this->_arguments[1]->evaluate($params);
+        // Check to see if this is zero.
+        if ($denom == 0) {
+            // Check the sign of the other argument and use to determine whether we return
+            // plus or minus infinity.
+            return INF * $this->_arguments[0]->evaluate($params);
+        } else {
+            $nume = $this->_arguments[0]->evaluate($params);
+            $rslt = fmod($nume, $denom);
+            return $rslt;
+        }
+    }
+
+    // Static class properties.
+    const NARGS = 2;
+    private static $formats = array(
+        'str' => '%s%%%s',
+        'tex' => '{%s}\%%{%s}'
+    );
+}
 
 /**
  * Class representing a multiplication operation in an algebraic expression.
@@ -1307,16 +1362,19 @@ class qtype_algebra_parser_function extends qtype_algebra_parser_term {
       *   functions are implemented without pseudonyms
       */
     public static $fnmap = array ();
-    public static $texmap = array('sqrt'  => '\\sqrt',
-                                  'log2'  => '\\log_{2}',
-                                  'log10' => '\\log_{10}',
-                                  'asin'  => '\\sin^{-1}',
-                                  'acos'  => '\\cos^{-1}',
-                                  'atan'  => '\\tan^{-1}',
-                                  'asinh' => '\\sinh^{-1}',
-                                  'acosh' => '\\cosh^{-1}',
-                                  'atanh' => '\\tanh^{-1}',
-                                  );
+    public static $texmap = array(
+        'floor'  => '\\mathrm{floor}',
+        'ceil'  => '\\mathrm{ceil}',
+        'sqrt'  => '\\sqrt',
+        'log2'  => '\\log_{2}',
+        'log10' => '\\log_{10}',
+        'asin'  => '\\sin^{-1}',
+        'acos'  => '\\cos^{-1}',
+        'atan'  => '\\tan^{-1}',
+        'asinh' => '\\sinh^{-1}',
+        'acosh' => '\\cosh^{-1}',
+        'atanh' => '\\tanh^{-1}',
+    );
 
     // List of functions requiring special brackets.
     public static $bracketmap = array ('sqrt'
@@ -1441,32 +1499,35 @@ class qtype_algebra_parser {
 
     // Functions which the parser will understand.
     // You have to implement any that are not standard PHP math functions.
-    public static $functions = array ('sqrt',
-                                      'exp',
-                                      'log2',
-                                      'ln',
-                                      'log',
-                                      'log10',
-                                      'sinh',
-                                      'cosh',
-                                      'tanh',
-                                      'sin',
-                                      'cos',
-                                      'tan',
-                                      'asin',
-                                      'acos',
-                                      'atan',
-                                      'asinh',
-                                      'acosh',
-                                      'atanh',
-                                      );
+    public static $functions = array (
+        'floor',
+        'ceil',
+        'sqrt',
+        'exp',
+        'log2',
+        'ln',
+        'log',
+        'log10',
+        'sinh',
+        'cosh',
+        'tanh',
+        'sin',
+        'cos',
+        'tan',
+        'asin',
+        'acos',
+        'atan',
+        'asinh',
+        'acosh',
+        'atanh',
+    );
 
     // Array to define the priority of the different operations. The parser implements the standard BODMAS priority:
     // brackets, order (power), division, mulitplication, addition, subtraction.
     private static $priority = array (
         array('qtype_algebra_parser_power'),
         array('qtype_algebra_parser_function'),
-        array('qtype_algebra_parser_divide', 'qtype_algebra_parser_multiply'),
+        array('qtype_algebra_parser_divide', 'qtype_algebra_parser_multiply', 'qtype_algebra_parser_modulo'),
         array('qtype_algebra_parser_add', 'qtype_algebra_parser_subtract')
     );
 
@@ -1493,6 +1554,7 @@ class qtype_algebra_parser {
         $this->_tokens = array (
             array ('/(\^|\*\*)/A',                            'qtype_algebra_parser_power'    )
             , array ('/\//A',                                 'qtype_algebra_parser_divide'   )
+            , array ('/%/A',                                  'qtype_algebra_parser_modulo'   )
             , array ('/\*/A',                                   'qtype_algebra_parser_multiply' )
             , array ('/\+/A',                                   'qtype_algebra_parser_add'      )
             , array ('/-/A',                                    'qtype_algebra_parser_subtract' )
-- 
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