bash - Why does printf (Unix) use round half down? -

why printf behave in such uncommon way?

> printf %.0f 2.5 > 2 > printf %.0f 2.51 > 3 

is there advantage of behaviour compensates probable misunderstandings (like this one)?

it's not strictly round-down:

> printf '%.0f\n' 2.5 2 > printf '%.0f\n' 3.5 4 

this form of rounding used combat bias if rounding large number of values; half of them rounded down, other half rounded up. rule is, round down if integer portion even, if integer portion odd.

---

this is, however, explanation of particular rounding scheme, not guaranteed used implementations of printf.