Shtifting bug explanation #134
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| The fields in bold are the fields that are changed. The exact implementation of this code is left to the reader. | ||
| The fields in bold are the fields that are changed. The exact implementation of this code is left to the reader. Please note that some books refers to this technique, calling it _coalescing_, but is the same concepts. |
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You should just introduce it as coalescing in the first place. It is already standard terminology in undergraduate curricula. So maybe early on, we could ask the question: what are some things we want to do with (free) heap blocks? The two natural answers are:
- Splitting -> motivate with an example
- Coalescing -> motivate with an example
The examples should show that splitting and coalescing go hand in hand. Imagine you only split, then your block sizes will be non-increasing, which means harder chance to repurpose free blocks. This is why coalescing is helpful.
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I just reread the whole paragraph, and the main thing is that the approach is basicall incremental, so the "coalesce" concept is only introduced by consecutive examples expanding the previous implementation, and i haven´t found a better place of where to introduce that name earlier. I'll try anyway to rephrase the paragraph.
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| This is one of the most misleading and subtle issue we can face while osdeving. And most of the time we face it the hard way. | ||
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| So what is the problem? let's imagine we have a 64 bit variable, and we need some to do a bitwise operation like `setting` the bit at the position `x`, this is easily achieved using the _left shift_ (`|=`) operator combined with a _xor_ (`|=`), like in the following pseudocode: |
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