gecko-dev/layout/style/generate-stylestructlist.py

#!/usr/bin/env python

# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

# This script generates nsStyleStructList.h, which contains macro invocations
# that can be used for three things:
#
# 1. To generate code for each inherited style struct.
# 2. To generate code for each reset style struct.
# 3. To generate a tree of nested if statements that can be used to run
#    some code on each style struct.
#
# As an example, if we assume that we have only four style structs, the
# generated tree of nested if statements looks like this:
#
#   if (STYLE_STRUCT_TEST < 4) {
#     if (STYLE_STRUCT_TEST < 2) {
#       if (STYLE_STRUCT_TEST == 0) {
#         ... code for style struct with id 0 ...
#       } else {
#         ... code for style struct with id 1 ...
#       }
#     } else {
#       if (STYLE_STRUCT_TEST == 2) {
#         ... code for style struct with id 2 ...
#       } else {
#         ... code for style struct with id 3 ...
#       }
#     }
#   }
#
# The TOPLEVELBRANCHES variable controls how widely we branch on the outermost
# if statement.  In the example above, it splits the search space in 2, but with
# a larger number of style structs to test -- particularly when the number is
# closer to one power of two than the next higher one -- the average number of
# comparisons can be reduced by splitting the top level check into more than 2.

import math

# List of style structs and their corresponding Check callback functions,
# if any.
STYLE_STRUCTS = [("INHERITED",) + x for x in [
    # Inherited style structs.
    ("Font",           "CheckFontCallback"),
    ("Color",          "CheckColorCallback"),
    ("List",           "nullptr"),
    ("Text",           "CheckTextCallback"),
    ("Visibility",     "nullptr"),
    ("Quotes",         "nullptr"),
    ("UserInterface",  "nullptr"),
    ("TableBorder",    "nullptr"),
    ("SVG",            "nullptr"),
]] + [("RESET",) + x for x in [
    # Reset style structs.
    ("Background",     "nullptr"),
    ("Position",       "nullptr"),
    ("TextReset",      "nullptr"),
    ("Display",        "nullptr"),
    ("Content",        "nullptr"),
    ("UIReset",        "nullptr"),
    ("Table",          "nullptr"),
    ("Margin",         "nullptr"),
    ("Padding",        "nullptr"),
    ("Border",         "nullptr"),
    ("Outline",        "nullptr"),
    ("XUL",            "nullptr"),
    ("SVGReset",       "nullptr"),
    ("Column",         "nullptr"),
]]

# How widely to branch on the outermost if statement.
TOPLEVELBRANCHES = 4


# ---- Generate nsStyleStructList.h ----

count = len(STYLE_STRUCTS)

def nextPowerOf2(x):
    return int(pow(2, math.ceil(math.log(x, 2))))

def printEntry(i):
    print "STYLE_STRUCT_%s(%s, %s)" % STYLE_STRUCTS[i]

def printTestTree(min, max, depth, branches):
    indent = "  " * depth
    if min == count - 1 and max >= count:
        print "  STYLE_STRUCT_TEST_CODE(%sNS_ASSERTION(STYLE_STRUCT_TEST == %d, \"out of range\");)" % (indent, min)
        printEntry(min)
    elif max - min == 2:
        print "  STYLE_STRUCT_TEST_CODE(%sif (STYLE_STRUCT_TEST == %d) {)" % (indent, min)
        printEntry(min)
        print "  STYLE_STRUCT_TEST_CODE(%s} else {)" % indent
        printEntry(min + 1)
        print "  STYLE_STRUCT_TEST_CODE(%s})" % indent
    elif min < count:
        mid = min + (max - min) / branches
        print "  STYLE_STRUCT_TEST_CODE(%sif (STYLE_STRUCT_TEST < %d) {)" % (indent, mid)
        printTestTree(min, mid, depth + 1, 2)
        for branch in range(1, branches):
            lo = min + branch * (max - min) / branches
            hi = min + (branch + 1) * (max - min) / branches
            if lo >= count:
                break
            if branch == branches - 1 or hi >= count:
                print "  STYLE_STRUCT_TEST_CODE(%s} else {)" % indent
            else:
                print "  STYLE_STRUCT_TEST_CODE(%s} else if (STYLE_STRUCT_TEST < %d) {)" % (indent, hi)
            printTestTree(lo, hi, depth + 1, 2)
        print "  STYLE_STRUCT_TEST_CODE(%s})" % indent

HEADER = """/* THIS FILE IS AUTOGENERATED BY generate-stylestructlist.py - DO NOT EDIT */

// IWYU pragma: private, include "nsStyleStructFwd.h"

/*
 * list of structs that contain the data provided by nsStyleContext, the
 * internal API for computed style data for an element
 */

/*
 * This file is intended to be used by different parts of the code, with
 * the STYLE_STRUCT macro (or the STYLE_STRUCT_INHERITED and
 * STYLE_STRUCT_RESET pair of macros) defined in different ways.
 */

#ifndef STYLE_STRUCT_INHERITED
#define STYLE_STRUCT_INHERITED(name, checkdata_cb) \\
  STYLE_STRUCT(name, checkdata_cb)
#define UNDEF_STYLE_STRUCT_INHERITED
#endif

#ifndef STYLE_STRUCT_RESET
#define STYLE_STRUCT_RESET(name, checkdata_cb) \\
  STYLE_STRUCT(name, checkdata_cb)
#define UNDEF_STYLE_STRUCT_RESET
#endif

#ifdef STYLE_STRUCT_TEST
#define STYLE_STRUCT_TEST_CODE(c) c
#else
#define STYLE_STRUCT_TEST_CODE(c)
#endif

// The inherited structs are listed before the Reset structs.
// nsStyleStructID assumes this is the case, and callers other than
// nsStyleStructFwd.h that want the structs in id-order just define
// STYLE_STRUCT rather than including the file twice.

"""
FOOTER = """
#ifdef UNDEF_STYLE_STRUCT_INHERITED
#undef STYLE_STRUCT_INHERITED
#undef UNDEF_STYLE_STRUCT_INHERITED
#endif

#ifdef UNDEF_STYLE_STRUCT_RESET
#undef STYLE_STRUCT_RESET
#undef UNDEF_STYLE_STRUCT_RESET
#endif

#undef STYLE_STRUCT_TEST_CODE
"""

print HEADER
printTestTree(0, nextPowerOf2(count), 0, TOPLEVELBRANCHES)
print FOOTER