diff -r 000000000000 -r 6474c204b198 layout/style/generate-stylestructlist.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/style/generate-stylestructlist.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,170 @@
+#!/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"),
+    ("Variables",      "CheckVariablesCallback"),
+]] + [("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