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Avoid pointer arithmetic on null pointer to remove undefined behavior

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The existing checks triggered undefined behavior when the stack was empty (null pointer). This change avoid this:
* If `stackTop_` and `stackEnd_` are null, it results in a `ptrdiff_t` of `0`
* If `stackTop_` and `stackEnd_` are valid pointers, they produce a `ptrdiff_t` with the remaining size on the stack
This commit is contained in:
Konstantin Käfer 2016-09-01 12:10:03 +02:00
parent 663f076c7b
commit 16872af889
1 changed files with 3 additions and 2 deletions
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5
include/rapidjson/internal/stack.h
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@ -17,6 +17,7 @@
#include "../allocators.h"
#include "swap.h"
#include <cstddef>
#if defined(__clang__)
RAPIDJSON_DIAG_PUSH
@ -114,7 +115,7 @@ public:
template<typename T>
RAPIDJSON_FORCEINLINE void Reserve(size_t count = 1) {
// Expand the stack if needed
if (RAPIDJSON_UNLIKELY(stackTop_ + sizeof(T) * count > stackEnd_))
if (RAPIDJSON_UNLIKELY(static_cast<std::ptrdiff_t>(sizeof(T) * count) > (stackEnd_ - stackTop_)))
Expand<T>(count);
}
@ -127,7 +128,7 @@ public:
template<typename T>
RAPIDJSON_FORCEINLINE T* PushUnsafe(size_t count = 1) {
RAPIDJSON_ASSERT(stackTop_);
RAPIDJSON_ASSERT(stackTop_ + sizeof(T) * count <= stackEnd_);
RAPIDJSON_ASSERT(static_cast<std::ptrdiff_t>(sizeof(T) * count) <= (stackEnd_ - stackTop_));
T* ret = reinterpret_cast<T*>(stackTop_);
stackTop_ += sizeof(T) * count;
return ret;