Thread: Division by zero error in to_char(num, '9.9EEEE')
While testing the numeric_power() patch in [1], I found this problem trying to use to_char() to format very small numbers: SELECT to_char(1.2e-1001, '9.9EEEE'); -- OK to_char ------------ 1.2e-1001 SELECT to_char(1.2e-1002, '9.9EEEE'); -- fails ERROR: division by zero It turns out that the problem is in get_str_from_var_sci() which attempts to divide the input by 1e-1002 to get the significand. However, it is using power_var_int() to compute 1e-1002, which has a maximum rscale of NUMERIC_MAX_DISPLAY_SCALE (1000), so it returns 0, which is the correct answer to that scale, and then get_str_from_var_sci() attempts to divide by that. Rather than messing with power_var_int(), I think the simplest solution is to just introduce a new local function, as in the attached patch. This directly constructs 10^n, for integer n, which is pretty trivial, and doesn't need any numeric multiplication or rounding. Regards, Dean [1] https://www.postgresql.org/message-id/CAEZATCUWUV_BP41Ob7QY12oF%2BqDxjTWfDpkdkcOOuojrDvOLxw%40mail.gmail.com
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On Fri, 30 Jul 2021 at 08:26, Dean Rasheed <dean.a.rasheed@gmail.com> wrote: > > SELECT to_char(1.2e-1002, '9.9EEEE'); -- fails > ERROR: division by zero > > I think the simplest > solution is to just introduce a new local function, as in the attached > patch. This directly constructs 10^n, for integer n, which is pretty > trivial, and doesn't need any numeric multiplication or rounding. > Unless there are any objections, I intend to push this shortly. I think it's a fairly straightforward bug fix, and I want to be able to use to_char() in some new numeric regression tests. Regards, Dean