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Diffstat (limited to 'security/sandbox/chromium/base/bit_cast.h')
| -rw-r--r-- | security/sandbox/chromium/base/bit_cast.h | 71 |
1 files changed, 0 insertions, 71 deletions
diff --git a/security/sandbox/chromium/base/bit_cast.h b/security/sandbox/chromium/base/bit_cast.h deleted file mode 100644 index b548467e7..000000000 --- a/security/sandbox/chromium/base/bit_cast.h +++ /dev/null @@ -1,71 +0,0 @@ -// Copyright 2016 The Chromium Authors. All rights reserved. -// Use of this source code is governed by a BSD-style license that can be -// found in the LICENSE file. - -#ifndef BASE_BIT_CAST_H_ -#define BASE_BIT_CAST_H_ - -#include <string.h> - -// bit_cast<Dest,Source> is a template function that implements the equivalent -// of "*reinterpret_cast<Dest*>(&source)". We need this in very low-level -// functions like the protobuf library and fast math support. -// -// float f = 3.14159265358979; -// int i = bit_cast<int32_t>(f); -// // i = 0x40490fdb -// -// The classical address-casting method is: -// -// // WRONG -// float f = 3.14159265358979; // WRONG -// int i = * reinterpret_cast<int*>(&f); // WRONG -// -// The address-casting method actually produces undefined behavior according to -// the ISO C++98 specification, section 3.10 ("basic.lval"), paragraph 15. -// (This did not substantially change in C++11.) Roughly, this section says: if -// an object in memory has one type, and a program accesses it with a different -// type, then the result is undefined behavior for most values of "different -// type". -// -// This is true for any cast syntax, either *(int*)&f or -// *reinterpret_cast<int*>(&f). And it is particularly true for conversions -// between integral lvalues and floating-point lvalues. -// -// The purpose of this paragraph is to allow optimizing compilers to assume that -// expressions with different types refer to different memory. Compilers are -// known to take advantage of this. So a non-conforming program quietly -// produces wildly incorrect output. -// -// The problem is not the use of reinterpret_cast. The problem is type punning: -// holding an object in memory of one type and reading its bits back using a -// different type. -// -// The C++ standard is more subtle and complex than this, but that is the basic -// idea. -// -// Anyways ... -// -// bit_cast<> calls memcpy() which is blessed by the standard, especially by the -// example in section 3.9 . Also, of course, bit_cast<> wraps up the nasty -// logic in one place. -// -// Fortunately memcpy() is very fast. In optimized mode, compilers replace -// calls to memcpy() with inline object code when the size argument is a -// compile-time constant. On a 32-bit system, memcpy(d,s,4) compiles to one -// load and one store, and memcpy(d,s,8) compiles to two loads and two stores. -// -// WARNING: if Dest or Source is a non-POD type, the result of the memcpy -// is likely to surprise you. - -template <class Dest, class Source> -inline Dest bit_cast(const Source& source) { - static_assert(sizeof(Dest) == sizeof(Source), - "bit_cast requires source and destination to be the same size"); - - Dest dest; - memcpy(&dest, &source, sizeof(dest)); - return dest; -} - -#endif // BASE_BIT_CAST_H_ |