Well, first of Stone Edge has an accuracy of 80. Reduced by 20% from Hustle (16) and you get an accuracy of 64.
Now, a single boost to accuracy is coded to actually 1.67 or + 67%, and then 2.0 or + 100% on the second. A single boost would mean 64 x 1.67, which equals 106.88. Pokemon tends to round down, so this likely means an accuracy of 106.
100 accuracy means it will always hit with no changes to accuracy or evasion, meaning this will always hit.
