The idea is that for long needles, you can discard their borders (the unaligned bits), search for the middle string using some efficient algorithm and only when it matches, check the borders

I get that. But even then, there is not "the middle bit", but rather 'eight middle bits' (and upto 7 different unaligned bits, at either end):

```haystack:
+                            *      *       *      *
1         2         3         4         5         6
+7         8         9         0         1         2
0123456789012345678901234567890123456789012345678901234567890123456789
+0123456789012345678901234567890123456789012345678901234567
1111000101001010110110101100101011101001010100010111100010011001010100
+0111111111001000000011100100100111011100100100111000110111
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bbbbbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmeee
bbbbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmeeee
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+m
bbbbbbbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
+me
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+mee
bbbbbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
+meee
bbbbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
+meeee
bbbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
+meeeee
bbmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
+meeeeee
bmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
+meeeeeee
mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
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