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Fix division-by-zero error in to_char() with 'EEEE' format.

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This fixes a long-standing bug when using to_char() to format a
numeric value in scientific notation -- if the value's exponent is
less than -NUMERIC_MAX_DISPLAY_SCALE-1 (-1001), it produced a
division-by-zero error.

The reason for this error was that get_str_from_var_sci() divides its
input by 10^exp, which it produced using power_var_int(). However, the
underflow test in power_var_int() causes it to return zero if the
result scale is too small. That's not a problem for power_var_int()'s
only other caller, power_var(), since that limits the rscale to 1000,
but in get_str_from_var_sci() the exponent can be much smaller,
requiring a much larger rscale. Fix by introducing a new function to
compute 10^exp directly, with no rscale limit. This also allows 10^exp
to be computed more efficiently, without any numeric multiplication,
division or rounding.

Discussion: https://postgr.es/m/CAEZATCWhojfH4whaqgUKBe8D5jNHB8ytzemL-PnRx+KCTyMXmg@mail.gmail.com
This commit is contained in:
Dean Rasheed
2021-08-05 09:27:35 +01:00
parent fa604e0dd0
commit ecbdbdfd90
3 changed files with 76 additions and 29 deletions
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7
src/test/regress/sql/numeric.sql
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@ -939,6 +939,13 @@ SELECT val,
to_char(val::float4, '9.999EEEE') as float4
FROM v;
WITH v(exp) AS
(VALUES(-16379),(-16378),(-1234),(-789),(-45),(-5),(-4),(-3),(-2),(-1),(0),
(1),(2),(3),(4),(5),(38),(275),(2345),(45678),(131070),(131071))
SELECT exp,
to_char(('1.2345e'||exp)::numeric, '9.999EEEE') as numeric
FROM v;
WITH v(val) AS
(VALUES('0'::numeric),('-4.2'),('4.2e9'),('1.2e-5'),('inf'),('-inf'),('nan'))
SELECT val,