Update to trunk

(bzr r11950.1.146)

4 files changed, 425 insertions, 447 deletions

diff --git a/src/util/expression-evaluator.cpp b/src/util/expression-evaluator.cpp
index dc59c67f4..3b7e77c6c 100644
--- a/src/util/expression-evaluator.cpp
+++ b/src/util/expression-evaluator.cpp
@@ -6,6 +6,7 @@
  * Copyright (C) 2008 Martin Nordholts <martinn@svn.gnome.org>
  * Modified for Inkscape by Johan Engelen
  * Copyright (C) 2011 Johan Engelen
+ * Copyright (C) 2013 Matthew Petroff
  *
  * This library is free software: you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -27,6 +28,7 @@
 #include "util/expression-evaluator.h"
 #include "util/units.h"
 
+#include <math.h>
 #include <string.h>
 
 using Inkscape::Util::unit_table;
@@ -34,495 +36,353 @@ using Inkscape::Util::unit_table;
 namespace Inkscape {
 namespace Util {
 
-enum
+EvaluatorQuantity::EvaluatorQuantity(double value, unsigned int dimension) :
+    value(value),
+    dimension(dimension)
 {
-  GIMP_EEVL_TOKEN_NUM        = 30000,
-  GIMP_EEVL_TOKEN_IDENTIFIER = 30001,
-
-  GIMP_EEVL_TOKEN_ANY        = 40000,
-
-  GIMP_EEVL_TOKEN_END        = 50000
-};
-
-typedef int GimpEevlTokenType;
-
-
-typedef struct
-{
-  GimpEevlTokenType type;
-
-  union
-  {
-    gdouble fl;
-
-    struct
-    {
-      const gchar *c;
-      gint         size;
-    };
-
-  } value;
-
-} GimpEevlToken;
+}
 
-typedef struct
+EvaluatorToken::EvaluatorToken()
 {
-  const gchar             *string;
-  GimpEevlUnitResolverProc unit_resolver_proc;
-  Unit                    *unit;
-
-  GimpEevlToken            current_token;
-  const gchar             *start_of_current_token;
-} GimpEevl;
+    type = 0;
+    value.fl = 0;
+}
 
-/** Unit Resolver...
- */
-static bool unitresolverproc  (const gchar* identifier, GimpEevlQuantity *result, Unit* unit)
+ExpressionEvaluator::ExpressionEvaluator(const char *string, Unit *unit) :
+    string(string),
+    unit(unit)
 {
-    if (!unit) {
-        result->value = 1;
-        result->dimension = 1;
-        return true;
-    }else if (!identifier) {
-        result->value = 1;
-        result->dimension = unit->isAbsolute() ? 1 : 0;
-        return true;
-    } else if (unit_table.hasUnit(identifier)) {
-        Unit identifier_unit = unit_table.getUnit(identifier);
-
-        // Catch the case of zero or negative unit factors (error!)
-        if (identifier_unit.factor < 0.0000001) {
-            return false;
-        }
-
-        result->value = unit->factor / identifier_unit.factor;
-        result->dimension = identifier_unit.isAbsolute() ? 1 : 0;
-        return true;
-    } else {
-        return false;
-    }
+    current_token.type  = TOKEN_END;
+    
+    // Preload symbol
+    parseNextToken();
 }
 
-static void             gimp_eevl_init                     (GimpEevl                 *eva,
-                                                            const gchar              *string,
-                                                            GimpEevlUnitResolverProc  unit_resolver_proc,
-                                                            Unit                     *unit);
-static GimpEevlQuantity gimp_eevl_complete                 (GimpEevl                 *eva);
-static GimpEevlQuantity gimp_eevl_expression               (GimpEevl                 *eva);
-static GimpEevlQuantity gimp_eevl_term                     (GimpEevl                 *eva);
-static GimpEevlQuantity gimp_eevl_signed_factor            (GimpEevl                 *eva);
-static GimpEevlQuantity gimp_eevl_factor                   (GimpEevl                 *eva);
-static gboolean         gimp_eevl_accept                   (GimpEevl                 *eva,
-                                                            GimpEevlTokenType         token_type,
-                                                            GimpEevlToken            *consumed_token);
-static void             gimp_eevl_lex                      (GimpEevl                 *eva);
-static void             gimp_eevl_lex_accept_count          (GimpEevl                 *eva,
-                                                            gint                      count,
-                                                            GimpEevlTokenType         token_type);
-static void             gimp_eevl_lex_accept_to             (GimpEevl                 *eva,
-                                                            gchar                    *to,
-                                                            GimpEevlTokenType         token_type);
-static void             gimp_eevl_move_past_whitespace     (GimpEevl                 *eva);
-static gboolean         gimp_eevl_unit_identifier_start    (gunichar                  c);
-static gboolean         gimp_eevl_unit_identifier_continue (gunichar                  c);
-static gint             gimp_eevl_unit_identifier_size     (const gchar              *s,
-                                                            gint                      start);
-static void             gimp_eevl_expect                   (GimpEevl                 *eva,
-                                                            GimpEevlTokenType         token_type,
-                                                            GimpEevlToken            *value);
-static void             gimp_eevl_error                    (GimpEevl                 *eva,
-                                                            const char               *msg);
-
-
 /**
  * Evaluates the given arithmetic expression, along with an optional dimension
  * analysis, and basic unit conversions.
  *
- * @param string              The NULL-terminated string to be evaluated.
- * @param unit_resolver_proc  Unit resolver callback.
- *
  * All units conversions factors are relative to some implicit
- * base-unit (which in GIMP is inches). This is also the unit of the
- * returned value.
+ * base-unit. This is also the unit of the returned value.
  *
- * Returns: A #GimpEevlQuantity with a value given in the base unit along with
- * the order of the dimension (i.e. if the base unit is inches, a dimension
- * order of two menas in^2).
+ * Returns: An EvaluatorQuantity with a value given in the base unit along with
+ * the order of the dimension (e.g. if the base unit is inches, a dimension
+ * order of two means in^2).
  *
  * @return Result of evaluation.
  * @throws Inkscape::Util::EvaluatorException There was a parse error.
  **/
-GimpEevlQuantity
-gimp_eevl_evaluate (const gchar* string, Unit* unit)
+EvaluatorQuantity ExpressionEvaluator::evaluate()
 {
-    if (! g_utf8_validate (string, -1, NULL)) {
+    if (!g_utf8_validate(string, -1, NULL)) {
         throw EvaluatorException("Invalid UTF8 string", NULL);
     }
-
-    GimpEevl eva;
-    gimp_eevl_init (&eva, string, unitresolverproc, unit);
-
-    return gimp_eevl_complete(&eva);
-}
-
-static void
-gimp_eevl_init (GimpEevl                  *eva,
-                const gchar               *string,
-                GimpEevlUnitResolverProc   unit_resolver_proc,
-                Unit                      *unit)
-{
-  eva->string              = string;
-  eva->unit_resolver_proc  = unit_resolver_proc;
-  eva->unit                = unit;
-
-  eva->current_token.type  = GIMP_EEVL_TOKEN_END;
-
-  /* Preload symbol... */
-  gimp_eevl_lex (eva);
-}
-
-static GimpEevlQuantity
-gimp_eevl_complete (GimpEevl *eva)
-{
-  GimpEevlQuantity result = {0, 0};
-  GimpEevlQuantity default_unit_factor;
-
-  /* Empty expression evaluates to 0 */
-  if (gimp_eevl_accept (eva, GIMP_EEVL_TOKEN_END, NULL))
-    return result;
-
-  result = gimp_eevl_expression (eva);
-
-  /* There should be nothing left to parse by now */
-  gimp_eevl_expect (eva, GIMP_EEVL_TOKEN_END, 0);
-
-  eva->unit_resolver_proc (NULL, &default_unit_factor, eva->unit);
-
-  /* Entire expression is dimensionless, apply default unit if
-   * applicable
-   */
-  if (result.dimension == 0 && default_unit_factor.dimension != 0)
-    {
-      result.value     /= default_unit_factor.value;
-      result.dimension  = default_unit_factor.dimension;
+    
+    EvaluatorQuantity result = EvaluatorQuantity();
+    EvaluatorQuantity default_unit_factor;
+    
+    // Empty expression evaluates to 0
+    if (acceptToken(TOKEN_END, NULL)) {
+        return result;
+    }
+    
+    result = evaluateExpression();
+    
+    // There should be nothing left to parse by now
+    isExpected(TOKEN_END, 0);
+    
+    resolveUnit(NULL, &default_unit_factor, unit);
+    
+    // Entire expression is dimensionless, apply default unit if applicable
+    if ( result.dimension == 0 && default_unit_factor.dimension != 0 ) {
+        result.value     /= default_unit_factor.value;
+        result.dimension  = default_unit_factor.dimension;
     }
-  return result;
+    return result;
 }
 
-static GimpEevlQuantity
-gimp_eevl_expression (GimpEevl *eva)
+EvaluatorQuantity ExpressionEvaluator::evaluateExpression()
 {
-  gboolean         subtract;
-  GimpEevlQuantity evaluated_terms;
-
-  evaluated_terms = gimp_eevl_term (eva);
-
-  /* continue evaluating terms, chained with + or -. */
-  for (subtract = FALSE;
-       gimp_eevl_accept (eva, '+', NULL) ||
-       (subtract = gimp_eevl_accept (eva, '-', NULL));
-       subtract = FALSE)
+    bool subtract;
+    EvaluatorQuantity evaluated_terms;
+    
+    evaluated_terms = evaluateTerm();
+    
+    // Continue evaluating terms, chained with + or -.
+    for (subtract = FALSE;
+        acceptToken('+', NULL) || (subtract = acceptToken('-', NULL));
+        subtract = FALSE)
     {
-      GimpEevlQuantity new_term = gimp_eevl_term (eva);
-
-      /* If dimensions missmatch, attempt default unit assignent */
-      if (new_term.dimension != evaluated_terms.dimension)
-        {
-          GimpEevlQuantity default_unit_factor;
-
-          eva->unit_resolver_proc (NULL,
-                                   &default_unit_factor,
-                                   eva->unit);
-
-          if (new_term.dimension == 0 &&
-              evaluated_terms.dimension == default_unit_factor.dimension)
+        EvaluatorQuantity new_term = evaluateTerm();
+        
+        // If dimensions mismatch, attempt default unit assignent
+        if ( new_term.dimension != evaluated_terms.dimension ) {
+            EvaluatorQuantity default_unit_factor;
+            
+            resolveUnit(NULL, &default_unit_factor, unit);
+            
+            if ( new_term.dimension == 0
+                && evaluated_terms.dimension == default_unit_factor.dimension )
             {
-              new_term.value     /= default_unit_factor.value;
-              new_term.dimension  = default_unit_factor.dimension;
-            }
-          else if (evaluated_terms.dimension == 0 &&
-                   new_term.dimension == default_unit_factor.dimension)
+                new_term.value     /= default_unit_factor.value;
+                new_term.dimension  = default_unit_factor.dimension;
+            } else if ( evaluated_terms.dimension == 0
+                && new_term.dimension == default_unit_factor.dimension )
             {
-              evaluated_terms.value     /= default_unit_factor.value;
-              evaluated_terms.dimension  = default_unit_factor.dimension;
-            }
-          else
-            {
-              gimp_eevl_error (eva, "Dimension missmatch during addition");
+                evaluated_terms.value     /= default_unit_factor.value;
+                evaluated_terms.dimension  = default_unit_factor.dimension;
+            } else {
+                throwError("Dimension mismatch during addition");
             }
         }
-
-      evaluated_terms.value += (subtract ? -new_term.value : new_term.value);
+        
+        evaluated_terms.value += (subtract ? -new_term.value : new_term.value);
     }
-
-  return evaluated_terms;
+    
+    return evaluated_terms;
 }
 
-static GimpEevlQuantity
-gimp_eevl_term (GimpEevl *eva)
+EvaluatorQuantity ExpressionEvaluator::evaluateTerm()
 {
-  gboolean         division;
-  GimpEevlQuantity evaluated_signed_factors;
-
-  evaluated_signed_factors = gimp_eevl_signed_factor (eva);
-
-  for (division = FALSE;
-       gimp_eevl_accept (eva, '*', NULL) ||
-       (division = gimp_eevl_accept (eva, '/', NULL));
-       division = FALSE)
+    bool division;
+    EvaluatorQuantity evaluated_exp_terms = evaluateExpTerm();
+    
+    for ( division = false;
+        acceptToken('*', NULL) || (division = acceptToken('/', NULL));
+        division = false )
     {
-      GimpEevlQuantity new_signed_factor = gimp_eevl_signed_factor (eva);
-
-      if (division)
-        {
-          evaluated_signed_factors.value     /= new_signed_factor.value;
-          evaluated_signed_factors.dimension -= new_signed_factor.dimension;
-
-        }
-      else
-        {
-          evaluated_signed_factors.value     *= new_signed_factor.value;
-          evaluated_signed_factors.dimension += new_signed_factor.dimension;
+        EvaluatorQuantity new_exp_term = evaluateExpTerm();
+        
+        if (division) {
+            evaluated_exp_terms.value     /= new_exp_term.value;
+            evaluated_exp_terms.dimension -= new_exp_term.dimension;
+        } else {
+            evaluated_exp_terms.value     *= new_exp_term.value;
+            evaluated_exp_terms.dimension += new_exp_term.dimension;
         }
     }
-
-  return evaluated_signed_factors;
-}
-
-static GimpEevlQuantity
-gimp_eevl_signed_factor (GimpEevl *eva)
-{
-  GimpEevlQuantity result;
-  gboolean         negate = FALSE;
-
-  if (! gimp_eevl_accept (eva, '+', NULL))
-    negate = gimp_eevl_accept (eva, '-', NULL);
-
-  result = gimp_eevl_factor (eva);
-
-  if (negate) result.value = -result.value;
-
-  return result;
+    
+    return evaluated_exp_terms;
 }
 
-static GimpEevlQuantity
-gimp_eevl_factor (GimpEevl *eva)
+EvaluatorQuantity ExpressionEvaluator::evaluateExpTerm()
 {
-  GimpEevlQuantity evaluated_factor = { 0, 0 };
-  GimpEevlToken    consumed_token;
-
-  if (gimp_eevl_accept (eva,
-                        GIMP_EEVL_TOKEN_NUM,
-                        &consumed_token))
-    {
-      evaluated_factor.value = consumed_token.value.fl;
-    }
-  else if (gimp_eevl_accept (eva, '(', NULL))
-    {
-      evaluated_factor = gimp_eevl_expression (eva);
-      gimp_eevl_expect (eva, ')', 0);
-    }
-  else
-    {
-      gimp_eevl_error (eva, "Expected number or '('");
-    }
-
-  if (eva->current_token.type == GIMP_EEVL_TOKEN_IDENTIFIER)
-    {
-      gchar            *identifier;
-      GimpEevlQuantity  result;
-
-      gimp_eevl_accept (eva,
-                        GIMP_EEVL_TOKEN_ANY,
-                        &consumed_token);
-
-      identifier = g_newa (gchar, consumed_token.value.size + 1);
-
-      strncpy (identifier, consumed_token.value.c, consumed_token.value.size);
-      identifier[consumed_token.value.size] = '\0';
-
-      if (eva->unit_resolver_proc (identifier,
-                                   &result,
-                                   eva->unit))
-        {
-          evaluated_factor.value      /= result.value;
-          evaluated_factor.dimension  += result.dimension;
-        }
-      else
-        {
-          gimp_eevl_error (eva, "Unit was not resolved");
+    EvaluatorQuantity evaluated_signed_factors = evaluateSignedFactor();
+    
+    while(acceptToken('^', NULL)) {
+        EvaluatorQuantity new_signed_factor = evaluateSignedFactor();
+        
+        if (new_signed_factor.dimension == 0) {
+            evaluated_signed_factors.value = pow(evaluated_signed_factors.value,
+                                                 new_signed_factor.value);
+            evaluated_signed_factors.dimension *= new_signed_factor.value;
+        } else {
+            throwError("Unit in exponent");
         }
     }
-
-  return evaluated_factor;
+    
+    return evaluated_signed_factors;
 }
 
-static gboolean
-gimp_eevl_accept (GimpEevl          *eva,
-                  GimpEevlTokenType  token_type,
-                  GimpEevlToken     *consumed_token)
+EvaluatorQuantity ExpressionEvaluator::evaluateSignedFactor()
 {
-  gboolean existed = FALSE;
-
-  if (token_type == eva->current_token.type ||
-      token_type == GIMP_EEVL_TOKEN_ANY)
-    {
-      existed = TRUE;
-
-      if (consumed_token)
-        *consumed_token = eva->current_token;
-
-      /* Parse next token */
-      gimp_eevl_lex (eva);
+    EvaluatorQuantity result;
+    bool negate = FALSE;
+    
+    if (!acceptToken('+', NULL)) {
+        negate = acceptToken ('-', NULL);
     }
-
-  return existed;
+    
+    result = evaluateFactor();
+    
+    if (negate) {
+        result.value = -result.value;
+    }
+    
+    return result;
 }
 
-static void
-gimp_eevl_lex (GimpEevl *eva)
+EvaluatorQuantity ExpressionEvaluator::evaluateFactor()
 {
-  const gchar *s;
-
-  gimp_eevl_move_past_whitespace (eva);
-  s = eva->string;
-  eva->start_of_current_token = s;
-
-  if (! s || s[0] == '\0')
-    {
-      /* We're all done */
-      eva->current_token.type = GIMP_EEVL_TOKEN_END;
-    }
-  else if (s[0] == '+' || s[0] == '-')
-    {
-      /* Snatch these before the g_strtod() does, othewise they might
-       * be used in a numeric conversion.
-       */
-      gimp_eevl_lex_accept_count (eva, 1, s[0]);
+    EvaluatorQuantity evaluated_factor = EvaluatorQuantity();
+    EvaluatorToken consumed_token = EvaluatorToken();
+    
+    if (acceptToken(TOKEN_NUM, &consumed_token)) {
+        evaluated_factor.value = consumed_token.value.fl;
+    } else if (acceptToken('(', NULL)) {
+        evaluated_factor = evaluateExpression();
+        isExpected(')', 0);
+    } else {
+        throwError("Expected number or '('");
     }
-  else
     
-    {
-      /* Attempt to parse a numeric value */
-      gchar  *endptr = NULL;
-      gdouble value      = g_strtod (s, &endptr);
-
-      if (endptr && endptr != s)
-        {
-          /* A numeric could be parsed, use it */
-          eva->current_token.value.fl = value;
-
-          gimp_eevl_lex_accept_to (eva, endptr, GIMP_EEVL_TOKEN_NUM);
+    if ( current_token.type == TOKEN_IDENTIFIER ) {
+        char *identifier;
+        EvaluatorQuantity result;
+        
+        acceptToken(TOKEN_ANY, &consumed_token);
+        
+        identifier = g_newa(char, consumed_token.value.size + 1);
+        
+        strncpy(identifier, consumed_token.value.c, consumed_token.value.size);
+        identifier[consumed_token.value.size] = '\0';
+        
+        if (resolveUnit(identifier, &result, unit)) {
+            evaluated_factor.value      /= result.value;
+            evaluated_factor.dimension  += result.dimension;
+        } else {
+            throwError("Unit was not resolved");
         }
-      else if (gimp_eevl_unit_identifier_start (s[0]))
-        {
-          /* Unit identifier */
-          eva->current_token.value.c    = s;
-          eva->current_token.value.size = gimp_eevl_unit_identifier_size (s, 0);
+    }
+    
+    return evaluated_factor;
+}
 
-          gimp_eevl_lex_accept_count (eva,
-                                      eva->current_token.value.size,
-                                      GIMP_EEVL_TOKEN_IDENTIFIER);
-        }
-      else
-        {
-          /* Everything else is a single character token */
-          gimp_eevl_lex_accept_count (eva, 1, s[0]);
+bool ExpressionEvaluator::acceptToken(TokenType token_type,
+                                      EvaluatorToken *consumed_token)
+{
+    bool existed = FALSE;
+    
+    if ( token_type == current_token.type || token_type == TOKEN_ANY ) {
+        existed = TRUE;
+        
+        if (consumed_token) {
+            *consumed_token = current_token;
         }
+        
+        // Parse next token
+        parseNextToken();
     }
+    
+    return existed;
 }
 
-static void
-gimp_eevl_lex_accept_count (GimpEevl          *eva,
-                            gint               count,
-                            GimpEevlTokenType  token_type)
+void ExpressionEvaluator::parseNextToken()
 {
-  eva->current_token.type  = token_type;
-  eva->string             += count;
+    const char *s;
+    
+    movePastWhiteSpace();
+    s = string;
+    start_of_current_token = s;
+    
+    if ( !s || s[0] == '\0' ) {
+        // We're all done
+        current_token.type = TOKEN_END;
+    } else if ( s[0] == '+' || s[0] == '-' ) {
+        // Snatch these before the g_strtod() does, othewise they might
+        // be used in a numeric conversion.
+        acceptTokenCount(1, s[0]);
+    } else {
+        // Attempt to parse a numeric value
+        char *endptr = NULL;
+        gdouble value = g_strtod(s, &endptr);
+        
+        if ( endptr && endptr != s ) {
+            // A numeric could be parsed, use it
+            current_token.value.fl = value;
+            
+            current_token.type = TOKEN_NUM;
+            string             = endptr;
+        } else if (isUnitIdentifierStart(s[0])) {
+            // Unit identifier
+            current_token.value.c = s;
+            current_token.value.size = getIdentifierSize(s, 0);
+            
+            acceptTokenCount(current_token.value.size, TOKEN_IDENTIFIER);
+        } else {
+            // Everything else is a single character token
+            acceptTokenCount(1, s[0]);
+        }
+    }
 }
 
-static void
-gimp_eevl_lex_accept_to (GimpEevl          *eva,
-                         gchar             *to,
-                         GimpEevlTokenType  token_type)
+void ExpressionEvaluator::acceptTokenCount (int count, TokenType token_type)
 {
-  eva->current_token.type = token_type;
-  eva->string             = to;
+    current_token.type  = token_type;
+    string             += count;
 }
 
-static void
-gimp_eevl_move_past_whitespace (GimpEevl *eva)
+void ExpressionEvaluator::isExpected(TokenType token_type,
+                                     EvaluatorToken *value)
 {
-  if (! eva->string)
-    return;
-
-  while (g_ascii_isspace (*eva->string))
-    eva->string++;
+    if (!acceptToken(token_type, value)) {
+        throwError("Unexpected token");
+    }
 }
 
-static gboolean
-gimp_eevl_unit_identifier_start (gunichar c)
+void ExpressionEvaluator::movePastWhiteSpace()
 {
-  return (g_unichar_isalpha (c) ||
-          c == (gunichar) '%'   ||
-          c == (gunichar) '\'');
+    if (!string) {
+        return;
+    }
+    
+    while (g_ascii_isspace(*string)) {
+        string++;
+    }
 }
 
-static gboolean
-gimp_eevl_unit_identifier_continue (gunichar c)
+bool ExpressionEvaluator::isUnitIdentifierStart(gunichar c)
 {
-  return (gimp_eevl_unit_identifier_start (c) ||
-          g_unichar_isdigit (c));
+    return (g_unichar_isalpha (c)
+        || c == (gunichar) '%'
+        || c == (gunichar) '\'');
 }
 
 /**
- * gimp_eevl_unit_identifier_size:
+ * getIdentifierSize:
  * @s:
  * @start:
  *
  * Returns: Size of identifier in bytes (not including NULL
  * terminator).
  **/
-static gint
-gimp_eevl_unit_identifier_size (const gchar *string,
-                                gint         start_offset)
+int ExpressionEvaluator::getIdentifierSize(const char *string, int start_offset)
 {
-  const gchar *start  = g_utf8_offset_to_pointer (string, start_offset);
-  const gchar *s      = start;
-  gunichar     c      = g_utf8_get_char (s);
-  gint         length = 0;
-
-  if (gimp_eevl_unit_identifier_start (c))
-    {
-      s = g_utf8_next_char (s);
-      c = g_utf8_get_char (s);
-      length++;
-
-      while (gimp_eevl_unit_identifier_continue (c))
-        {
-          s = g_utf8_next_char (s);
-          c = g_utf8_get_char (s);
-          length++;
+    const char *start  = g_utf8_offset_to_pointer(string, start_offset);
+    const char *s      = start;
+    gunichar    c      = g_utf8_get_char(s);
+    int         length = 0;
+    
+    if (isUnitIdentifierStart(c)) {
+        s = g_utf8_next_char (s);
+        c = g_utf8_get_char (s);
+        length++;
+        
+        while ( isUnitIdentifierStart (c) || g_unichar_isdigit (c) ) {
+            s = g_utf8_next_char(s);
+            c = g_utf8_get_char(s);
+            length++;
         }
     }
-  
-  return g_utf8_offset_to_pointer (start, length) - start;
+    
+    return g_utf8_offset_to_pointer(start, length) - start;
 }
 
-static void
-gimp_eevl_expect (GimpEevl          *eva,
-                  GimpEevlTokenType  token_type,
-                  GimpEevlToken     *value)
+bool ExpressionEvaluator::resolveUnit (const char* identifier,
+                                       EvaluatorQuantity *result,
+                                       Unit* unit)
 {
-  if (! gimp_eevl_accept (eva, token_type, value))
-    gimp_eevl_error (eva, "Unexpected token");
+    if (!unit) {
+        result->value = 1;
+        result->dimension = 1;
+        return true;
+    }else if (!identifier) {
+        result->value = 1;
+        result->dimension = unit->isAbsolute() ? 1 : 0;
+        return true;
+    } else if (unit_table.hasUnit(identifier)) {
+        Unit identifier_unit = unit_table.getUnit(identifier);
+        result->value = Quantity::convert(1, *unit, identifier_unit);
+        result->dimension = identifier_unit.isAbsolute() ? 1 : 0;
+        return true;
+    } else {
+        return false;
+    }
 }
 
-static void
-gimp_eevl_error (GimpEevl *eva,
-                 const char    *msg)
+void ExpressionEvaluator::throwError(const char *msg)
 {
-  throw EvaluatorException(msg, eva->start_of_current_token);
+    throw EvaluatorException(msg, start_of_current_token);
 }
 
 } // namespace Util
diff --git a/src/util/expression-evaluator.h b/src/util/expression-evaluator.h
index 4b1065268..6412dfea7 100644
--- a/src/util/expression-evaluator.h
+++ b/src/util/expression-evaluator.h
@@ -6,6 +6,7 @@
  * Copyright (C) 2008-2009 Martin Nordholts <martinn@svn.gnome.org>
  * Modified for Inkscape by Johan Engelen
  * Copyright (C) 2011 Johan Engelen
+ * Copyright (C) 2013 Matthew Petroff
  *
  * This library is free software: you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -22,8 +23,8 @@
  * <http://www.gnu.org/licenses/>.
  */
 
-#ifndef SEEN_GIMP_EEVL_H
-#define SEEN_GIMP_EEVL_H
+#ifndef INKSCAPE_UTIL_EXPRESSION_EVALUATOR_H
+#define INKSCAPE_UTIL_EXPRESSION_EVALUATOR_H
 
 #include "util/units.h"
 
@@ -33,7 +34,7 @@
 
 /**
  * @file
- * Introducing eevl eva, the evaluator. A straightforward recursive
+ * Expression evaluator: A straightforward recursive
  * descent parser, no fuss, no new dependencies. The lexer is hand
  * coded, tedious, not extremely fast but works. It evaluates the
  * expression as it goes along, and does not create a parse tree or
@@ -43,8 +44,8 @@
  *
  * It relies on external unit resolving through a callback and does
  * elementary dimensionality constraint check (e.g. "2 mm + 3 px * 4
- * in" is an error, as L + L^2 is a missmatch). It uses g_strtod() for numeric
- * conversions and it's non-destructive in terms of the paramters, and
+ * in" is an error, as L + L^2 is a mismatch). It uses g_strtod() for numeric
+ * conversions and it's non-destructive in terms of the parameters, and
  * it's reentrant.
  *
  * EBNF:
@@ -52,7 +53,9 @@
  *   expression    ::= term { ('+' | '-') term }*  |
  *                     <empty string> ;
  *
- *   term          ::= signed factor { ( '*' | '/' ) signed factor }* ;
+ *   term          ::= exponent { ( '*' | '/' ) exponent }* ;
+ *
+ *   exponent      ::= signed factor { '^' signed factor }* ;
  *
  *   signed factor ::= ( '+' | '-' )? factor ;
  *
@@ -79,37 +82,104 @@ namespace Util {
 class Unit;
 
 /**
-* GimpEevlQuantity:
-* @value: In reference units.
-* @dimension: in has a dimension of 1, in^2 has a dimension of 2 etc
-*/
-typedef struct
+ * EvaluatorQuantity:
+ * @param value         In reference units.
+ * @param dimension     mm has a dimension of 1, mm^2 has a dimension of 2, etc.
+ */
+class EvaluatorQuantity
 {
+public:
+    EvaluatorQuantity(double value = 0, unsigned int dimension = 0);
+    
     double value;
-    gint dimension;
-} GimpEevlQuantity;
+    unsigned int dimension;
+};
 
-typedef bool (* GimpEevlUnitResolverProc) (const gchar      *identifier,
-                                               GimpEevlQuantity *result,
-                                               Unit* unit);
+/**
+ * TokenType
+ */
+enum {
+  TOKEN_NUM        = 30000,
+  TOKEN_IDENTIFIER = 30001,
+  TOKEN_ANY        = 40000,
+  TOKEN_END        = 50000
+};
+typedef int TokenType;
 
-GimpEevlQuantity gimp_eevl_evaluate (const gchar* string, Unit* unit = NULL);
+/**
+ * EvaluatorToken
+ */
+class EvaluatorToken
+{
+public:
+    EvaluatorToken();
+    
+    TokenType type;
+    
+    union {
+        double fl;
+        struct {
+            const char *c;
+            int size;
+        };
+    } value;
+};
+
+/**
+ * ExpressionEvaluator
+ * @param string    NULL terminated input string to evaluate
+ * @param unit      Unit output should be in
+ */
+class ExpressionEvaluator
+{
+public:
+    ExpressionEvaluator(const char *string, Unit *unit = NULL);
+    
+    EvaluatorQuantity evaluate();
+
+private:
+    const char *string;
+    Unit *unit;
+    
+    EvaluatorToken current_token;
+    const char *start_of_current_token;
+    
+    EvaluatorQuantity evaluateExpression();
+    EvaluatorQuantity evaluateTerm();
+    EvaluatorQuantity evaluateExpTerm();
+    EvaluatorQuantity evaluateSignedFactor();
+    EvaluatorQuantity evaluateFactor();
+    
+    bool acceptToken(TokenType token_type, EvaluatorToken *consumed_token);
+    void parseNextToken();
+    void acceptTokenCount(int count, TokenType token_type);
+    void isExpected(TokenType token_type, EvaluatorToken *value);
+    
+    void movePastWhiteSpace();
+    
+    static bool isUnitIdentifierStart(gunichar c);
+    static int getIdentifierSize(const char *s, int start);
+    
+    static bool resolveUnit(const char *identifier, EvaluatorQuantity *result, Unit *unit);
+    
+    void throwError(const char *msg);
+};
 
 /**
  * Special exception class for the expression evaluator.
  */
 class EvaluatorException : public std::exception {
 public:
-    EvaluatorException(const char * message, const char *at_position) {
+    EvaluatorException(const char *message, const char *at_position) {
         std::ostringstream os;
-        const char* token = at_position ? at_position : "<End of input>";
+        const char *token = at_position ? at_position : "<End of input>";
         os << "Expression evaluator error: " << message << " at '" << token << "'";
         msgstr = os.str();
     }
 
     virtual ~EvaluatorException() throw() {} // necessary to destroy the string object!!!
 
-    virtual const char* what() const throw () {
+    virtual const char *what() const throw () {
         return msgstr.c_str();
     }
 protected:
@@ -119,4 +189,4 @@ protected:
 }
 }
 
-#endif // SEEN_GIMP_EEVL_H
+#endif // INKSCAPE_UTIL_EXPRESSION_EVALUATOR_H
diff --git a/src/util/units.cpp b/src/util/units.cpp
index 3fdd77916..e5c6f74fb 100644
--- a/src/util/units.cpp
+++ b/src/util/units.cpp
@@ -114,6 +114,7 @@ Unit::Unit(UnitType type,
     abbr(abbr),
     description(description)
 {
+    g_return_if_fail(factor <= 0);
 }
 
 void Unit::clear()
@@ -166,25 +167,25 @@ bool operator!= (const Unit &u1, const Unit &u2)
 int Unit::svgUnit() const
 {
     if (!abbr.compare("px"))
-        return 1;
+        return SVGLength::PX;
     if (!abbr.compare("pt"))
-        return 2;
+        return SVGLength::PT;
     if (!abbr.compare("pc"))
-        return 3;
+        return SVGLength::PC;
     if (!abbr.compare("mm"))
-        return 4;
+        return SVGLength::MM;
     if (!abbr.compare("cm"))
-        return 5;
+        return SVGLength::CM;
     if (!abbr.compare("in"))
-        return 6;
+        return SVGLength::INCH;
     if (!abbr.compare("ft"))
-        return 7;
+        return SVGLength::FOOT;
     if (!abbr.compare("em"))
-        return 8;
+        return SVGLength::EM;
     if (!abbr.compare("ex"))
-        return 9;
+        return SVGLength::EX;
     if (!abbr.compare("%"))
-        return 10;
+        return SVGLength::PERCENT;
     return 0;
 }
 
@@ -220,6 +221,36 @@ Unit UnitTable::getUnit(Glib::ustring const &unit_abbr) const
         return Unit();
     }
 }
+Unit UnitTable::getUnit(SVGLength::Unit const u) const
+{
+    Glib::ustring u_str;
+    switch(u) {
+        case SVGLength::PX:
+            u_str = "px"; break;
+        case SVGLength::PT:
+            u_str = "pt"; break;
+        case SVGLength::PC:
+            u_str = "pc"; break;
+        case SVGLength::MM:
+            u_str = "mm"; break;
+        case SVGLength::CM:
+            u_str = "cm"; break;
+        case SVGLength::INCH:
+            u_str = "in"; break;
+        case SVGLength::FOOT:
+            u_str = "ft"; break;
+        case SVGLength::EM:
+            u_str = "em"; break;
+        case SVGLength::EX:
+            u_str = "ex"; break;
+        case SVGLength::PERCENT:
+            u_str = "%"; break;
+        default:
+            u_str = "";
+    }
+    
+    return getUnit(u_str);
+}
 
 Quantity UnitTable::getQuantity(Glib::ustring const& q) const
 {
@@ -421,6 +452,27 @@ double Quantity::convert(const double from_dist, const Glib::ustring from, const
     return convert(from_dist, unit_table.getUnit(from), unit_table.getUnit(to));
 }
 
+bool operator< (const Quantity &ql, const Quantity &qr)
+{
+    if (ql.unit->type != qr.unit->type) {
+        g_warning("Incompatible units");
+        return false;
+    }
+    return ql.quantity < qr.value(*ql.unit);
+}
+bool operator> (const Quantity &ql, const Quantity &qr)
+{
+    if (ql.unit->type != qr.unit->type) {
+        g_warning("Incompatible units");
+        return false;
+    }
+    return ql.quantity > qr.value(*ql.unit);
+}
+bool operator!= (const Quantity &q1, const Quantity &q2)
+{
+    return (*q1.unit != *q2.unit) || (q1.quantity != q2.quantity);
+}
+
 } // namespace Util
 } // namespace Inkscape
 
diff --git a/src/util/units.h b/src/util/units.h
index bb202b96a..7ba6e1e86 100644
--- a/src/util/units.h
+++ b/src/util/units.h
@@ -1,5 +1,6 @@
 /*
  * Inkscape Units
+ * These classes are used for defining different unit systems.
  *
  * Authors:
  *   Matthew Petroff <matthew@mpetroff.net>
@@ -9,25 +10,12 @@
  * Released under GNU GPL, read the file 'COPYING' for more information
  */
 
-/*
-This is a rough draft of a global 'units' thingee, to allow dialogs and
-the ruler to share info about unit systems...  Dunno if this is the
-right kind of object though, so we may have to redo this or shift things
-around later when it becomes clearer what we need.
-
-This object is used for defining different unit systems.
-
-This is intended to eventually replace inkscape/helper/units.*.
-
-Need to review the Units support that's in Gtkmm already...
-
-*/
-
 #ifndef INKSCAPE_UTIL_UNITS_H
 #define INKSCAPE_UTIL_UNITS_H
 
 #include <map>
 #include <glibmm/ustring.h>
+#include "svg/svg-length.h"
 
 namespace Inkscape {
 namespace Util {
@@ -112,6 +100,11 @@ public:
     static double convert(const double from_dist, const Glib::ustring from, const Unit &to);
     static double convert(const double from_dist, const Unit &from, const Glib::ustring to);
     static double convert(const double from_dist, const Glib::ustring from, const Glib::ustring to);
+    
+    /** Comparison operators. */
+    friend bool operator< (const Quantity &ql, const Quantity &qr);
+    friend bool operator> (const Quantity &ql, const Quantity &qr);
+    friend bool operator!= (const Quantity &q1, const Quantity &q2);
 };
 
 class UnitTable {
@@ -132,6 +125,9 @@ class UnitTable {
     /** Retrieve a given unit based on its string identifier */
     Unit    getUnit(Glib::ustring const &name) const;
     
+    /** Retrieve a given unit based on its SVGLength unit */
+    Unit    getUnit(SVGLength::Unit const u) const;
+    
     /** Retrieve a quantity based on its string identifier */
     Quantity getQuantity(Glib::ustring const &q) const;