哪个高手进来帮我注释一段代码；

[youzhipeng]

void* AlignedMemory::allocate(size_t size, size_t alignment)
{
assert(0 < alignment && alignment <= 128 && Bitwise::isPO2(alignment));
//为什么要范围限制？

unsigned char* p = new unsigned char[size + alignment];
size_t offset = alignment - (size_t(p) & (alignment-1)); //什么意思？

unsigned char* result = p + offset;
result[-1] = (unsigned char)offset; //不懂？

return result;
}
//---------------------------------------------------------------------
void* AlignedMemory::allocate(size_t size)
{
return allocate(size, OGRE_SIMD_ALIGNMENT);
}
//---------------------------------------------------------------------
void AlignedMemory::deallocate(void* p)
{
if (p)
{
unsigned char* mem = (unsigned char*)p;
mem = mem - mem[-1];
delete [] mem;
}
}

[youzhipeng]

/** Allocate memory with given alignment.
@param
size The size of memory need to allocate.
@param
alignment The alignment of result pointer, must be power of two
and in range [1, 128].
@returns
The allocated memory pointer.
@par
On failure, exception will be throw.
*/
static void* allocate(size_t size, size_t alignment);

/** Allocate memory with default platform dependent alignment.
@remarks
The default alignment depend on target machine, this function
guarantee aligned memory according with SIMD processing and
cache boundary friendly.
@param
size The size of memory need to allocate.
@returns
The allocated memory pointer.
@par
On failure, exception will be throw.
*/ static void* allocate(size_t size);

/** Deallocate memory that allocated by this class.
@param
p Pointer to the memory allocated by this class or <b>NULL</b> pointer.
@par
On <b>NULL</b> pointer, nothing happen.
*/ static void deallocate(void* p);