Merge pull request rarestype#123 from rarestype/internalize-exp10

[patch]: internalize and colocate the exp10 table with the module that actually uses it

Author: tayloraswift

Sources/JSONAST/JSON.Number.Base10.Inverse.swift

@@ -1,10 +1,9 @@
 extension JSON.Number {
-    /// A namespace for decimal-related functionality.
-    ///
-    /// This API is used by library functions that are emitted into the client.
-    /// Most library users should not have to call it directly.
-    public enum Base10 {
-        /// Positive powers of 10, up to `10_000_000_000_000_000_000`.
+    @available(
+        *, deprecated, message: """
+        JSON.Number.Base10 is deprecated and will be removed in a future release
+        """
+    ) public enum Base10 {
         public static let Exp: [UInt64] = [
             1,
             10,

Sources/JSONAST/JSON.Number.Base10.swift

@@ -0,0 +1,36 @@
+extension JSON.Number {
+    /// A namespace for decimal-related functionality.
+    enum Exp10 {}
+}
+extension JSON.Number.Exp10 {
+    static var startIndex: Int { 0 }
+    static var endIndex: Int { 20 }
+
+    static subscript(power: Int) -> UInt64 {
+        switch power {
+        case 0: 1
+        case 1: 10
+        case 2: 100
+        case 3: 1_000
+        case 4: 10_000
+        case 5: 100_000
+        case 6: 1_000_000
+        case 7: 10_000_000
+        case 8: 100_000_000
+        case 9: 1_000_000_000
+        case 10: 10_000_000_000
+        case 11: 100_000_000_000
+        case 12: 1_000_000_000_000
+        case 13: 10_000_000_000_000
+        case 14: 100_000_000_000_000
+        case 15: 1_000_000_000_000_000
+        case 16: 10_000_000_000_000_000
+        case 17: 100_000_000_000_000_000
+        case 18: 1_000_000_000_000_000_000
+        case 19: 10_000_000_000_000_000_000
+        default: fatalError("power out of representable range")
+        //  UInt64.max:
+        //  18_446_744_073_709_551_615
+        }
+    }
+}

Sources/JSONParsing/Rules/JSON.Number.Exp10.swift

@@ -119,9 +119,9 @@ extension JSON.NumberRule: ParsingRule {
                     places = 0
                 }
 
-                if  shift < JSON.Number.Base10.Exp.endIndex,
+                if  shift < JSON.Number.Exp10.endIndex,
                     case (let shifted, false) = units.multipliedReportingOverflow(
-                        by: JSON.Number.Base10.Exp[shift]
+                        by: JSON.Number.Exp10[shift]
                     ) {
                     units = shifted
                 } else {