There's a way to level memory. Equation is always overexpenditure, but it's necessary to make an effective use of the kash. In addition, some systems cannot correctly use if the double word is on two memory pages at the same time, an exception. An exception could be processed by an additional programme which allowed the conflict to -- but such treatment significantly slowed the programme. Equation is used to ensure that the programme does not slow down.// allocate aligned memory
void *internal_align_malloc(size_t size, size_t n)
This size is the size of the block that will receive the program. n is the level of equity.I'll show you the 4.Адрес Нужный адрес Итог addr + n - 1) & (~(n - 1)) x100 Выделено
0 0 или 4 4 или 8 байт 4 104 (4)8
1 4..7 5 байт 4 101 7
2 4..7 6 байт 4 102 6
3 4..7 7 байт 4 103 5
Since the difference between 7 and 8 is not large, the case of 0 (Otogo 4) is generally not used because the algorithm is complicated. A simpler option 4 (outcome is applied. The outcome means how much it takes to keep a 4-bite low.It turns out that if we have a four-bate equalization, it's gonna take four to eight byte. But we'll get the address on the way out, and we don't know what size we're gonna have, so we're taking it to the maximum with the spare. So, we're asking for 8 byte, after processing, there'll be four, and four will go to overhead. Even though the first program got more byte, it doesn't count. The programme is considered to have received as much as it has requested by calling a function. You can give it to me again (though it's not theoretical, but practically no byte in the bayte) no less.Now we're looking for 100 whites. We're going to need between 101 and 104 byte for 100 byte. It's like we're gonna need a hundred byte across 4 bytes.Four more bikes are wasted to keep the address that returned the malloc invested to do free. That's what we got. need = 100 + 4 + 4 = 108♪ Puncture free will also have to be summoned through the envelope, the return of internal_align_malloc is an undesirable result (not all memory managers can identify a single piece in the middle of the interval, it's accepted that the address that returned malloc should be sent free.While it is often more than necessary, it is not recommended to use more if there is no function (to get a "capacity" to call it a characteristic), which will give a real memory to a given site. i.e., if 100 is allocated, 100 rather than 101, or 102. If you try to write more, you can accidentally "destruct your memory" and the program will fly or work incorrectly.If you have to remembrance more, there are two algorithms (a) to create a new era of memory, and to re-copulate the old, old section to free. (b) to call relloc "realloc" if that function is available. (In fact, relloc makes the first).Theoretically-Baythic statues can be used, but in practice they rarely do so because if the station is released, the statue is cancelled. But there are tumors, it's when malloc is made, and free is never. But I'm afraid the storage of every single free bayt will need at least four bays of information that can be packed, but these operations will be quite complicated, so the statues are usually not used. If you have a self-writing relloc, it's worth taking account of the rest of your tail, and if they ask to extend your memory to the balance and less, the same area can be returned.Now, as the address is recorded at the station. Let's give you an address.Then after the change, you have an address dst equal to 8.
Then dst - sizeof(char*) = address 4.Pro char**♪ Transformation of indicator.Let's addr = 4. If you can record the number int, you need to translate the address to the type of indicator into int, and you need to open the index through the (star operator) to put it in value. I mean. (int*)addr - it's an indication of an address that can be revealed as int, then one can be written in. *(int*)addr = 1 or ((int*)addr)[0] = 1♪Now, we want to write down the index. char *ptr (pr) He has a type. char*♪ To record ptr at the address, you need to get an address to the type indicator. char*, i.e. (char**)addr♪ Total attribution can be done *(char**)(addr)=ptr♪ Now, instead of addr, the phrase dst - sizeof(char*) and received *(char**)(dst - sizeof(char*)) = ptr♪