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libbase: remove ARRAYSIZE_UNSAFE.

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Also fix the indentation of a neighboring comment.

Bug: N/A
Test: builds
Change-Id: Iebe5f518b2ac14718f3cae91007e62b61bed9dc0
This commit is contained in:
Elliott Hughes 2018-10-24 14:34:52 -07:00
parent 48a0e186a7
commit 514edae27c
1 changed files with 14 additions and 54 deletions
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68
base/include/android-base/macros.h
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@ -75,46 +75,6 @@ char(&ArraySizeHelper(T(&array)[N]))[N]; // NOLINT(readability/casting)
#define arraysize(array) (sizeof(ArraySizeHelper(array)))
// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize,
// but can be used on anonymous types or types defined inside
// functions. It's less safe than arraysize as it accepts some
// (although not all) pointers. Therefore, you should use arraysize
// whenever possible.
//
// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type
// size_t.
//
// ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error
//
// "warning: division by zero in ..."
//
// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer.
// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays.
//
// The following comments are on the implementation details, and can
// be ignored by the users.
//
// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in
// the array) and sizeof(*(arr)) (the # of bytes in one array
// element). If the former is divisible by the latter, perhaps arr is
// indeed an array, in which case the division result is the # of
// elements in the array. Otherwise, arr cannot possibly be an array,
// and we generate a compiler error to prevent the code from
// compiling.
//
// Since the size of bool is implementation-defined, we need to cast
// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final
// result has type size_t.
//
// This macro is not perfect as it wrongfully accepts certain
// pointers, namely where the pointer size is divisible by the pointee
// size. Since all our code has to go through a 32-bit compiler,
// where a pointer is 4 bytes, this means all pointers to a type whose
// size is 3 or greater than 4 will be (righteously) rejected.
#define ARRAYSIZE_UNSAFE(a) \
((sizeof(a) / sizeof(*(a))) / \
static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))
#define SIZEOF_MEMBER(t, f) sizeof(std::declval<t>().f)
// Changing this definition will cause you a lot of pain. A majority of
@ -153,23 +113,23 @@ void UNUSED(const T&...) {
// case 42:
// ...
//
// As shown in the example above, the FALLTHROUGH_INTENDED macro should be
// followed by a semicolon. It is designed to mimic control-flow statements
// like 'break;', so it can be placed in most places where 'break;' can, but
// only if there are no statements on the execution path between it and the
// next switch label.
// As shown in the example above, the FALLTHROUGH_INTENDED macro should be
// followed by a semicolon. It is designed to mimic control-flow statements
// like 'break;', so it can be placed in most places where 'break;' can, but
// only if there are no statements on the execution path between it and the
// next switch label.
//
// When compiled with clang, the FALLTHROUGH_INTENDED macro is expanded to
// [[clang::fallthrough]] attribute, which is analysed when performing switch
// labels fall-through diagnostic ('-Wimplicit-fallthrough'). See clang
// documentation on language extensions for details:
// http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough
// When compiled with clang, the FALLTHROUGH_INTENDED macro is expanded to
// [[clang::fallthrough]] attribute, which is analysed when performing switch
// labels fall-through diagnostic ('-Wimplicit-fallthrough'). See clang
// documentation on language extensions for details:
// http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough
//
// When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no
// effect on diagnostics.
// When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no
// effect on diagnostics.
//
// In either case this macro has no effect on runtime behavior and performance
// of code.
// In either case this macro has no effect on runtime behavior and performance
// of code.
#ifndef FALLTHROUGH_INTENDED
#define FALLTHROUGH_INTENDED [[clang::fallthrough]] // NOLINT
#endif