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- User-level malloc
- -----------------
- The user-level malloc implementation is defined to be simple, not
- fast or efficient. It uses a very basic first-fit block algorithm.
- There's an 8-byte header which holds the offsets to the previous
- and next blocks, a used/free bit, and some magic numbers (for
- consistency checking) in the remaining available header bits. It also
- allocates in units of 8 bytes to guarantee proper alignment of
- doubles. (It also assumes its own headers are aligned on 8-byte
- boundaries.)
- On malloc(), it searches the entire heap starting at the beginning
- for the first block big enough to hold the allocation. If it doesn't
- find one, it calls sbrk() to get more memory. If it does find one, it
- marks the block in use. It splits the remaining portion of the block
- off as a new free block only if said portion is large enough to hold
- both a header and some data.
- On free(), it marks the block free and then tries to merge it with
- the adjacent blocks (both above and below) if they're free.
- That's about all there is to it.
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