switchgenerator.java

java中比较著名的js引擎当属mozilla开源的rhino

/* -*- Mode: java; tab-width: 4; indent-tabs-mode: 1; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Igor Bukanov
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */
package org.mozilla.javascript.tools.idswitch;

import org.mozilla.javascript.EvaluatorException;
import org.mozilla.javascript.tools.ToolErrorReporter;

public class SwitchGenerator {

    String v_switch_label = "L0";
    String v_label = "L";
    String v_s = "s";
    String v_c = "c";
    String v_guess = "X";
    String v_id = "id";
    String v_length_suffix = "_length";

    int use_if_threshold = 3;
    int char_tail_test_threshold = 2;

    private IdValuePair[] pairs;
    private String default_value;
    private int[] columns;
    private boolean c_was_defined;

    private CodePrinter P;
    private ToolErrorReporter R;
    private String source_file;

    public CodePrinter getCodePrinter() { return P; }
    public void setCodePrinter(CodePrinter value) { P = value; }

    public ToolErrorReporter getReporter() { return R; }
    public void setReporter(ToolErrorReporter value) { R = value; }

    public String getSourceFileName() { return source_file; }
    public void setSourceFileName(String value) { source_file = value; }

    public void generateSwitch(String[] pairs, String default_value) {
        int N = pairs.length / 2;
        IdValuePair[] id_pairs = new IdValuePair[N];
        for (int i = 0; i != N; ++i) {
            id_pairs[i] = new IdValuePair(pairs[2 * i], pairs[2 * i + 1]);
        }
        generateSwitch(id_pairs, default_value);

    }

    public void generateSwitch(IdValuePair[] pairs, String default_value) {
        int begin = 0;
        int end = pairs.length;
        if (begin == end) { return; }
        this.pairs = pairs;
        this.default_value = default_value;

        generate_body(begin, end, 2);
    }

    private void generate_body(int begin, int end, int indent_level) {
        P.indent(indent_level);
        P.p(v_switch_label); P.p(": { ");
        P.p(v_id); P.p(" = "); P.p(default_value);
        P.p("; String "); P.p(v_guess); P.p(" = null;");

        c_was_defined = false;
        int c_def_begin = P.getOffset();
        P.p(" int "); P.p(v_c); P.p(';');
        int c_def_end = P.getOffset();
        P.nl();

        generate_length_switch(begin, end, indent_level + 1);

        if (!c_was_defined) {
            P.erase(c_def_begin, c_def_end);
        }

        P.indent(indent_level + 1);
        P.p("if ("); P.p(v_guess); P.p("!=null && ");
        P.p(v_guess); P.p("!="); P.p(v_s);
        P.p(" && !"); P.p(v_guess); P.p(".equals("); P.p(v_s); P.p(")) ");
        P.p(v_id); P.p(" = "); P.p(default_value); P.p(";"); P.nl();
        P.line(indent_level, "}");
    }

    private void generate_length_switch(int begin, int end, int indent_level) {

        sort_pairs(begin, end, -1);

        check_all_is_different(begin, end);

        int lengths_count = count_different_lengths(begin, end);

        columns = new int[pairs[end  - 1].idLength];

        boolean use_if;
        if (lengths_count <= use_if_threshold) {
            use_if = true;
            if (lengths_count != 1) {
                P.indent(indent_level);
                P.p("int "); P.p(v_s); P.p(v_length_suffix);
                P.p(" = "); P.p(v_s); P.p(".length();");
                P.nl();
            }
        }
        else {
            use_if = false;
            P.indent(indent_level);
            P.p(v_label); P.p(": switch (");
            P.p(v_s); P.p(".length()) {");
            P.nl();
        }

        int same_length_begin = begin;
        int cur_l = pairs[begin].idLength, l = 0;
        for (int i = begin;;) {
            ++i;
            if (i == end || (l = pairs[i].idLength) != cur_l) {
                int next_indent;
                if (use_if) {
                    P.indent(indent_level);
                    if (same_length_begin != begin) { P.p("else "); }
                    P.p("if (");
                    if (lengths_count == 1) {
                        P.p(v_s); P.p(".length()==");
                    }
                    else {
                        P.p(v_s); P.p(v_length_suffix); P.p("==");
                    }
                    P.p(cur_l);
                    P.p(") {");
                    next_indent = indent_level + 1;
                }
                else {
                    P.indent(indent_level);
                    P.p("case "); P.p(cur_l); P.p(":");
                    next_indent = indent_level + 1;
                }
                generate_letter_switch
                    (same_length_begin, i, next_indent, !use_if, use_if);
                if (use_if) {
                    P.p("}"); P.nl();
                }
                else {
                    P.p("break "); P.p(v_label); P.p(";"); P.nl();
                }

                if (i == end) { break; }
                same_length_begin = i;
                cur_l = l;
            }
        }

        if (!use_if) {
            P.indent(indent_level); P.p("}"); P.nl();
        }

    }

    private void generate_letter_switch
        (int begin, int end,
         int indent_level, boolean label_was_defined, boolean inside_if)
    {
        int L = pairs[begin].idLength;

        for (int i = 0; i != L; ++i) {
            columns[i] = i;
        }

        generate_letter_switch_r
            (begin, end, L, indent_level, label_was_defined, inside_if);
    }


    private boolean generate_letter_switch_r
        (int begin, int end, int L,
         int indent_level, boolean label_was_defined, boolean inside_if)
    {
        boolean next_is_unreachable = false;
        if (begin + 1 == end) {
            P.p(' ');
            IdValuePair pair = pairs[begin];
            if (L > char_tail_test_threshold) {
                P.p(v_guess); P.p("="); P.qstring(pair.id); P.p(";");
                P.p(v_id); P.p("="); P.p(pair.value); P.p(";");
            }
            else {
                if (L == 0) {
                    next_is_unreachable = true;
                    P.p(v_id); P.p("="); P.p(pair.value);
                    P.p("; break "); P.p(v_switch_label); P.p(";");
                }
                else {
                    P.p("if (");
                    int column = columns[0];
                    P.p(v_s); P.p(".charAt("); P.p(column); P.p(")==");
                    P.qchar(pair.id.charAt(column));
                    for (int i = 1; i != L; ++i) {
                        P.p(" && ");
                        column = columns[i];
                        P.p(v_s); P.p(".charAt("); P.p(column); P.p(")==");
                        P.qchar(pair.id.charAt(column));
                    }
                    P.p(") {");
                    P.p(v_id); P.p("="); P.p(pair.value);
                    P.p("; break "); P.p(v_switch_label); P.p(";}");
                }
            }
            P.p(' ');
            return next_is_unreachable;
        }