### string_helpers: fix precision loss for some inputs

It was noticed that we lose precision in the final calculation for some inputs. The most egregious example is size=3000 blk_size=1900 in units of 10 should yield 5.70 MB but in fact yields 3.00 MB (oops). This is because the current algorithm doesn't correctly account for all the remainders in the logarithms. Fix this by doing a correct calculation in the remainders based on napier's algorithm. Additionally, now we have the correct result, we have to account for arithmetic rounding because we're printing 3 digits of precision. This means that if the fourth digit is five or greater, we have to round up, so add a section to ensure correct rounding. Finally account for all possible inputs correctly, including zero for block size. Fixes: b9f28d86Signed-off-by: James Bottomley <JBottomley@Odin.com> Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: <stable@vger.kernel.org> [delay until after 4.4 release] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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