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alloc/stack: fix allocation record offset calculation

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This commit is contained in:
Danny Robson 2017-01-04 22:40:52 +11:00
parent a63e6c213e
commit faf7e68671
1 changed files with 11 additions and 10 deletions
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19
alloc/stack.cpp
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@ -38,7 +38,7 @@ union record {
using offset_t = uint32_t;
char *as_bytes;
offset_t *as_uint32;
offset_t *as_offset;
};
@ -58,26 +58,26 @@ stack::allocate (size_t bytes)
void*
stack::allocate (size_t bytes, size_t alignment)
{
alignment = util::max (MIN_ALIGNMENT, alignment);
// reserve space at the front of the allocation to record the total
// allocation size so we can account for alignment if required.
auto ptr = m_cursor + sizeof (record::offset_t);
// align the outgoing pointer if required
alignment = util::max (MIN_ALIGNMENT, alignment);
ptr = align (ptr, alignment);
// ensure we haven't overrun our allocated segment
if (ptr + bytes > m_end)
throw std::bad_alloc ();
// store the total size and record the new stack head
// use a 'record' struct as a window into the reserved space at the front
// of the allocation and store the offset to the previous allocation head
// (from the record struct). allows us to account for alignment.
record record;
record.as_bytes = ptr - sizeof (record::offset_t);
*record.as_uint32 = trunc_cast<uint32_t> (ptr - m_cursor);
*record.as_offset = trunc_cast<uint32_t> (ptr - m_cursor);
m_cursor = ptr + bytes;
return ptr;
}
@ -103,10 +103,11 @@ stack::deallocate (void *_ptr, size_t bytes, size_t alignment)
record record;
record.as_bytes = ptr - sizeof (record::offset_t);
CHECK_LE (bytes, *record.as_uint32);
CHECK_GE (m_cursor - *record.as_uint32, m_begin);
//CHECK_LE (bytes, *record.as_offset);
CHECK_GE (m_cursor - *record.as_offset, m_begin);
m_cursor -= *record.as_uint32 + bytes;
m_cursor -= bytes;
m_cursor -= *record.as_offset;
}