From bc66cfa70e54f81732d868ad6ac376c9c2764efe Mon Sep 17 00:00:00 2001
From: Volker Berlin <volker.berlin@googlemail.com>
Date: Fri, 11 May 2018 11:55:55 +0200
Subject: [PATCH] Add a local variable manager

---
 .../module/LocaleVariableManager.java         | 150 ++++++++++++++++++
 1 file changed, 150 insertions(+)
 create mode 100644 src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java

diff --git a/src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java b/src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java
new file mode 100644
index 0000000..b72969d
--- /dev/null
+++ b/src/de/inetsoftware/jwebassembly/module/LocaleVariableManager.java
@@ -0,0 +1,150 @@
+/*
+   Copyright 2018 Volker Berlin (i-net software)
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+*/
+package de.inetsoftware.jwebassembly.module;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import de.inetsoftware.jwebassembly.WasmException;
+
+/**
+ * This manager monitor the locale variables of a method to create a translation from the slot based index in Java to
+ * the variable based index in WebAssembly. An 8-byte variable of type long and double consumes in Java 2 slots, but
+ * only one index in WebAssmenbly.
+ * 
+ * @author Volker Berlin
+ *
+ */
+class LocaleVariableManager {
+
+    private LocaleVariable[]     variables;
+
+    private int                  size;
+
+    private ArrayList<ValueType> localTypes = new ArrayList<>();
+
+    /**
+     * Create a new instance.
+     */
+    LocaleVariableManager() {
+        // initialize with a initial capacity that should be enough for the most methods
+        variables = new LocaleVariable[8];
+        for( int i = 0; i < variables.length; i++ ) {
+            variables[i] = new LocaleVariable();
+        }
+    }
+
+    /**
+     * Reset the manager to an initial state
+     */
+    void reset() {
+        for( int i = 0; i < size; i++ ) {
+            LocaleVariable var = variables[i];
+            var.valueType = null;
+            var.idx = -1;
+        }
+        size = 0;
+    }
+
+    /**
+     * Mark a variable slot as used with its type.
+     * 
+     * @param valueType
+     *            the type of the local variable
+     * @param slot
+     *            the memory/slot index of the local variable
+     */
+    void use( ValueType valueType, int slot ) {
+        ensureCapacity( slot );
+        size = Math.max( size, slot + 1 );
+        LocaleVariable var = variables[slot];
+        if( var.valueType != null && var.valueType != valueType ) {
+            throw new WasmException( "Redefine local variable type from " + var.valueType + " to "
+                            + valueType, null, -1 );
+        }
+        var.valueType = valueType;
+    }
+
+    /**
+     * Calculate the WebAssembly index position on the consumed data.
+     */
+    void calculate() {
+        int idx = 0;
+        for( int i = 0; i < size; i++ ) {
+            LocaleVariable var = variables[i];
+            if( var.valueType == null ) { // unused slot or extra slot for double and long values 
+                continue;
+            }
+            var.idx = idx++;
+        }
+    }
+
+    /**
+     * Get the data types of the local variables. The value is only valid until the next call.
+     * 
+     * @param paramCount
+     *            the count of method parameter which should be exclude
+     * @return the reused list with fresh values
+     */
+    List<ValueType> getLocalTypes( int paramCount ) {
+        localTypes.clear();
+        for( int i = 0; i < size; i++ ) {
+            LocaleVariable var = variables[i];
+            if( var.idx >= paramCount ) {
+                localTypes.add( var.valueType );
+            }
+        }
+        return localTypes;
+    }
+
+    /**
+     * Get the WebAssembly variable index of the given Java Slot.
+     * 
+     * @param slot
+     *            the memory/slot index of the local variable in Java
+     * @return the variable index in WebAssembly
+     */
+    int get( int slot ) {
+        return variables[slot].idx;
+    }
+
+    /**
+     * Ensure that there is enough capacity.
+     * 
+     * @param slot
+     *            the needed slot
+     */
+    private void ensureCapacity( int slot ) {
+        if( slot >= variables.length ) {
+            int i = variables.length;
+            variables = Arrays.copyOf( variables, slot + 1 );
+            for( ; i < variables.length; i++ ) {
+                variables[i] = new LocaleVariable();
+            }
+        }
+    }
+
+    /**
+     * The state of a single local variable slot.
+     */
+    private static class LocaleVariable {
+        private ValueType valueType;
+
+        private int       idx = -1;
+    }
+}