Optimize Uri.percentDecode. (#2149)

* Optimize Uri.percentDecode.

* Tweak test case.

coil-core/src/commonMain/kotlin/coil3/Uri.common.kt

@@ -138,16 +138,19 @@ private fun parseUri(data: String): Uri {
         fragment = data.substring(fragmentStartIndex, data.length)
     }
 
-    val size = maxOf(
-        scheme.length,
-        authority.length,
+    val maxLength = maxOf(
+        0,
         maxOf(
-            path.length,
-            query.length,
-            fragment.length,
-        ),
+            scheme.length,
+            authority.length,
+            maxOf(
+                path.length,
+                query.length,
+                fragment.length,
+            ),
+        ) - 2,
     )
-    val bytes = ByteArray(size)
+    val bytes = ByteArray(maxLength)
     return Uri(
         data = data,
         scheme = scheme?.percentDecode(bytes),
@@ -161,9 +164,19 @@ private fun parseUri(data: String): Uri {
 private fun String.percentDecode(bytes: ByteArray): String {
     var size = 0
     var index = 0
-
-    while (index < length) {
-        if (get(index) == '%' && index + 2 < length) {
+    val length = length
+    val searchLength = maxOf(0, length - 2)
+
+    while (true) {
+        if (index >= searchLength) {
+            if (index == size) {
+                // Fast path: the string doesn't have any encoded characters.
+                return this
+            } else if (index >= length) {
+                // Slow path: decode the byte array.
+                return bytes.decodeToString(endIndex = size)
+            }
+        } else if (get(index) == '%') {
             try {
                 val hex = substring(index + 1, index + 3)
                 bytes[size] = hex.toInt(16).toByte()
@@ -177,14 +190,6 @@ private fun String.percentDecode(bytes: ByteArray): String {
         size++
         index++
     }
-
-    if (size == length) {
-        // Fast path: the string doesn't have any encoded characters.
-        return this
-    } else {
-        // Slow path: decode the byte array.
-        return bytes.decodeToString(endIndex = size)
-    }
 }
 
 private val String?.length: Int

coil-core/src/commonTest/kotlin/coil3/UriTest.kt

@@ -75,6 +75,19 @@ class UriTest {
         assertEquals(string, uri.toString())
     }
 
+    @Test
+    fun encodedSingle() {
+        val string = "https://example.com/something%20"
+        val uri = string.toUri()
+        assertEquals("https", uri.scheme)
+        assertEquals("example.com", uri.authority)
+        assertEquals("/something ", uri.path)
+        assertEquals(listOf("something "), uri.pathSegments)
+        assertNull(uri.query)
+        assertNull(uri.fragment)
+        assertEquals(string, uri.toString())
+    }
+
     @Test
     fun encodedMalformed() {
         val string = "https://example.com/%E4%B8%8A%E6%B5%B7%2B%E4%B8%AD%E5%9C%8B%"