When writting or reading a block, if the block doesn't fit the area where it begins, the next base address is always zero. Thus the calculations to define the next value of addr are unnecessary.
Here's a quick validity proof using the previous calculations:
First: Considering the case where the block doesn't fit it's first area:
That means that (count + addr > length), what makes:
count = length - addr; (1)
So the following operations:
addr += count;
addr -= length;
Are the same as doing:
addr = addr + count - length; (2)
Using (1) and (2) we have:
addr = addr + length - addr - length = 0
Second: When the block fits the area where it's at:
That means that variable count is not changed,
thus (n -= count) evaluates to 0, which makes the loop exit.
Another change was (b += count;) being moved after the condition to break the loop, since we just need to move the block pointer when it doesn't fit the first area.
Gustavo Jose de Sousa
Andrew Tridgell
Randy Mackay
Andrew Tridgell