Enhance parser and add a few functions, fix hex parsing (#4)

1. Unify all numbers under double type
A bit lazy, but is easily maintainable. Precision is enough for most use cases.

2. Add more functions
Add `num`, `parselit`, `str`.

3. Fix hex parser error
Previously the "0x" was greedy and matches single zeros, which then raised a parsing error because it couldn't match a hex number.

Reviewed-on: #4

src/Parser/XnParser.cs

@@ -78,15 +78,22 @@ namespace XNeedle.Parser
                                                         string.Join(",", parameters.Select(e => e.Type.Name))));
         }
 
+        // This needs to match as one atomic token, else with a separate String("0x") the 0 is consumed,
+        // which triggers a parsing error on single zero numbers
         public static readonly Parser<string> HexNumber = 
-            from prefix in Parse.String("0x").Token()
+            Parse.Regex(@"0x[0-9a-fA-F]+").Token()
-            from number in Parse.Char(char.IsAsciiHexDigit, "hexadecimal digit").AtLeastOnce().Text()
+                .Select(s => s.Substring(2));
-            select number;
+
+        public static readonly Parser<string> BooleanLiteral =
+            from value in Parse.String("true").XOr(Parse.String("false")).Text()
+            select value;
 
         static readonly Parser<Expression> NumberConstant =
-            HexNumber.Select(x => Expression.Constant(int.Parse(x, System.Globalization.NumberStyles.HexNumber)))
+            HexNumber.Select(x => Expression.Constant((double)int.Parse(x, System.Globalization.NumberStyles.HexNumber)))
+            .XOr(BooleanLiteral.Select(x => Expression.Constant(x == "true" ? 1.0 : 0.0)))
             .XOr(Parse.Decimal.Select(x => Expression.Constant(double.Parse(x))))
             .Named("number");
+        
 
         private static readonly Parser<Expression> StringConstant =
             from open in Parse.Char('"')

src/Transformation/ContextFunctions.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using System.Linq;
 using System.Text;
 using Sprache;
@@ -12,12 +13,54 @@ namespace XNeedle.Transformation
 {
     public class ContextFunctions
     {
-        public static string hexlit(Context ctx, int value)
+
+        public static double num(Context ctx, string value, double numbase = 10)
+        {
+            if (string.IsNullOrWhiteSpace(value))
+            {
+                return 0;
+            }
+
+            string cleanedValue = value.Trim();
+
+            if (numbase != 10)
+            {
+                cleanedValue = cleanedValue.TrimStart('0');
+                cleanedValue = cleanedValue.TrimStart('x');
+
+                // Convert to Int64 to not lose any fidelity
+                return Convert.ToInt64(cleanedValue, (int)numbase);
+            }
+
+            return double.Parse(cleanedValue, CultureInfo.InvariantCulture);
+        }
+        public static string str(Context ctx, double value, double numbase = 10)
+        {
+            if (numbase == 10)
+            {
+                return $"{value}";
+            }
+
+            // Ignore fraction for other bases by casting to long
+            return Convert.ToString((long)value, (int)numbase);
+        }
+
+        public static string hexlit(Context ctx, double value)
         {
             uint v = (uint)value;
             return $"#x{v:x8}";
         }
 
+        public static double parselit(Context ctx, string literal, double numbase = 16)
+        {
+            if (string.IsNullOrWhiteSpace(literal) || literal.Length <= 2)
+            {
+                throw new ArgumentException($"Cannot parse literal \"{literal}\"");
+            }
+
+            return (double)Convert.ToInt32(literal.Substring(2), (int)numbase);
+        }
+
         public static string lower(Context ctx, string text)
         {
             return text.ToLower();
@@ -70,7 +113,7 @@ namespace XNeedle.Transformation
             return reflected;
         }
 
-        public static int crc32(Context ctx, int poly = 0x04C11DB7, int init = 0, int xorOut = 0, bool reflected = false)
+        public static double crc32(Context ctx, double poly = 0x04C11DB7, double init = 0, double xorOut = 0, double reflected = 0.0)
         {
             if (ctx.Node is null)
                 return 0;
@@ -88,7 +131,7 @@ namespace XNeedle.Transformation
             byte[] fragBytes = Encoding.UTF8.GetBytes(data);
 
             // Step 3: Digest into CRC32 using parameterized CRC32 - by default MPEG-2
-            return (int)ComputeCrc32(fragBytes, (uint)poly, (uint)init, (uint)xorOut, reflected);
+            return (double)ComputeCrc32(fragBytes, (uint)poly, (uint)init, (uint)xorOut, reflected == 1.0);
         }
 
         public static string text(Context ctx)