Support all digit chars on JS and Native #KT-46002

libraries/tools/kotlin-stdlib-gen/src/generators/unicode/ranges/writers/DigitRangesWriter.kt

@@ -21,10 +21,16 @@ internal class DigitRangesWriter(private val strategy: RangesWritingStrategy) :
         writer.appendLine()
         writer.appendLine(binarySearchRange())
         writer.appendLine()
+        writer.appendLine(digitToIntImpl())
+        writer.appendLine()
         writer.appendLine(isDigitImpl())
     }
 
     private fun binarySearchRange(): String = """
+        /**
+         * Returns the index of the largest element in [array] smaller or equal to the specified [needle],
+         * or -1 if [needle] is smaller than the smallest element in [array].
+         */
         internal fun binarySearchRange(array: IntArray, needle: Int): Int {
             var bottom = 0
             var top = array.size - 1
@@ -44,17 +50,29 @@ internal class DigitRangesWriter(private val strategy: RangesWritingStrategy) :
         }
         """.trimIndent()
 
-    private fun isDigitImpl(): String {
+    private fun digitToIntImpl(): String {
         val rangeStart = strategy.rangeRef("rangeStart")
+        return """
+        /**
+         * Returns an integer from 0..9 indicating the digit this character represents,
+         * or -1 if this character is not a digit.
+         */
+        internal fun Char.digitToIntImpl(): Int {
+            val ch = this.code
+            val index = binarySearchRange($rangeStart, ch)
+            val diff = ch - $rangeStart[index]
+            return if (diff < 10) diff else -1
+        }
+        """.trimIndent()
+    }
+
+    private fun isDigitImpl(): String {
         return """
         /**
          * Returns `true` if this character is a digit.
          */
         internal fun Char.isDigitImpl(): Boolean {
-            val ch = this.code
-            val index = binarySearchRange($rangeStart, ch)
-            val high = $rangeStart[index] + 9
-            return ch <= high
+            return digitToIntImpl() >= 0
         }
         """.trimIndent()
     }