mfbt/MacroArgs.h@97036ab72558
mfbt/MacroArgs.h
Tue, 06 Jan 2015 21:39:09 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Tue, 06 Jan 2015 21:39:09 +0100
- branch
- TOR_BUG_9701
- changeset 8
- 97036ab72558
- permissions
- -rw-r--r--
Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.
1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
7 /*
8 * Implements various macros meant to ease the use of variadic macros.
9 */
11 #ifndef mozilla_MacroArgs_h
12 #define mozilla_MacroArgs_h
14 /*
15 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) counts the number of variadic
16 * arguments and prefixes it with |aPrefix|. For example:
17 *
18 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(, foo, 42) expands to 2
19 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(A, foo, 42, bar) expands to A3
20 *
21 * You must pass in between 1 and 50 (inclusive) variadic arguments, past
22 * |aPrefix|. It is not legal to do
23 *
24 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(prefix)
25 *
26 * (that is, pass in 0 variadic arguments). To ensure that a compile-time
27 * error occurs when these constraints are violated, use the
28 * MOZ_STATIC_ASSERT_VALID_ARG_COUNT macro with the same variaidc arguments
29 * wherever this macro is used.
30 *
31 * Passing (__VA_ARGS__, <rest of arguments>) rather than simply calling
32 * MOZ_MACROARGS_ARG_COUNT_HELPER2(__VA_ARGS__, <rest of arguments>) very
33 * carefully tiptoes around a MSVC bug where it improperly expands __VA_ARGS__
34 * as a single token in argument lists. For details, see:
35 *
36 * http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement
37 * http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644
38 */
39 #define MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) \
40 MOZ_MACROARGS_ARG_COUNT_HELPER((__VA_ARGS__, \
41 aPrefix##50, aPrefix##49, aPrefix##48, aPrefix##47, aPrefix##46, \
42 aPrefix##45, aPrefix##44, aPrefix##43, aPrefix##42, aPrefix##41, \
43 aPrefix##40, aPrefix##39, aPrefix##38, aPrefix##37, aPrefix##36, \
44 aPrefix##35, aPrefix##34, aPrefix##33, aPrefix##32, aPrefix##31, \
45 aPrefix##30, aPrefix##29, aPrefix##28, aPrefix##27, aPrefix##26, \
46 aPrefix##25, aPrefix##24, aPrefix##23, aPrefix##22, aPrefix##21, \
47 aPrefix##20, aPrefix##19, aPrefix##18, aPrefix##17, aPrefix##16, \
48 aPrefix##15, aPrefix##14, aPrefix##13, aPrefix##12, aPrefix##11, \
49 aPrefix##10, aPrefix##9, aPrefix##8, aPrefix##7, aPrefix##6, \
50 aPrefix##5, aPrefix##4, aPrefix##3, aPrefix##2, aPrefix##1, aPrefix##0))
52 #define MOZ_MACROARGS_ARG_COUNT_HELPER(aArgs) \
53 MOZ_MACROARGS_ARG_COUNT_HELPER2 aArgs
55 #define MOZ_MACROARGS_ARG_COUNT_HELPER2( \
56 a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, \
57 a11, a12, a13, a14, a15, a16, a17, a18, a19, a20, \
58 a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, \
59 a31, a32, a33, a34, a35, a36, a37, a38, a39, a40, \
60 a41, a42, a43, a44, a45, a46, a47, a48, a49, a50, \
61 a51, ...) a51
63 /*
64 * MOZ_STATIC_ASSERT_VALID_ARG_COUNT ensures that a compile-time error occurs
65 * when the argument count constraints of MOZ_PASTE_PREFIX_AND_ARG_COUNT are
66 * violated. Use this macro wherever MOZ_PASTE_PREFIX_AND_ARG_COUNT is used
67 * and pass it the same variadic arguments.
68 *
69 * This macro employs a few dirty tricks to function. To detect the zero
70 * argument case, |(__VA_ARGS__)| is stringified, sizeof-ed, and compared to
71 * what it should be in the absence of arguments.
72 *
73 * Detecting too many arguments is a little trickier. With a valid argument
74 * count and a prefix of 1, MOZ_PASTE_PREFIX_AND_ARG_COUNT expands to e.g. 14.
75 * With a prefix of 0.0, it expands to e.g. 0.04. If there are too many
76 * arguments, it expands to the first argument over the limit. If this
77 * exceeding argument is a number, the assertion will fail as there is no
78 * number than can simultaneously be both > 10 and < 0.1. If the exceeding
79 * argument is not a number, a compile-time error will still occur because the
80 * exceeding argument is compared to an int and a double.
81 */
82 #define MOZ_MACROARGS_STRINGIFY_HELPER(x) #x
83 #define MOZ_STATIC_ASSERT_VALID_ARG_COUNT(...) \
84 static_assert( \
85 sizeof(MOZ_MACROARGS_STRINGIFY_HELPER((__VA_ARGS__))) != sizeof("()") && \
86 (MOZ_PASTE_PREFIX_AND_ARG_COUNT(1, __VA_ARGS__)) > 10 && \
87 (MOZ_PASTE_PREFIX_AND_ARG_COUNT(0.0, __VA_ARGS__)) < 0.1, \
88 "MOZ_STATIC_ASSERT_VALID_ARG_COUNT requires 1 to 50 arguments") /* ; */
90 /*
91 * MOZ_ARGS_AFTER_N expands to its arguments excluding the first |N|
92 * arguments. For example:
93 *
94 * MOZ_ARGS_AFTER_2(a, b, c, d) expands to: c, d
95 */
96 #define MOZ_ARGS_AFTER_1(a1, ...) __VA_ARGS__
97 #define MOZ_ARGS_AFTER_2(a1, a2, ...) __VA_ARGS__
99 /*
100 * MOZ_ARG_N expands to its |N|th argument.
101 */
102 #define MOZ_ARG_1(a1, ...) a1
103 #define MOZ_ARG_2(a1, a2, ...) a2
105 #endif /* mozilla_MacroArgs_h */
