SV: SV: Bug in printf ?

Peter J. Acklam pjacklam@online.no
Thu Jun 30 14:23:00 GMT 2005


Dave Korn wrote:

> Have you considered that your sunblade might be operating
> in a different rounding mode, by default?

I didn't know there were different rounding modes.
I thought everyone used so-called "unbiased rounding",
so I'm sorry for adding confusion.

> I would imagine that printf may well work under-the-hood
> by shifting the desired decimal places above the point,
> rounding to integer, and printing out that number.

Could be.  I haven't dug into those matters, but your
suggestion certainly makes sense.

Anyway, the following line

   seq -4.5 1 4.5 | while read x; do printf '%4s -> %3.0f\n' $x $x; done

which gives

   -4.5 ->  -4
   -3.5 ->  -3
   -2.5 ->  -2
   -1.5 ->  -1
   -0.5 ->  -1
    0.5 ->   1
    1.5 ->   1
    2.5 ->   2
    3.5 ->   3
    4.5 ->   4

suggests that printf rounds towards zero, but something
funny happens for -0.5 and 0.5.

Peter

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