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

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

1 files changed, 8 insertions, 0 deletions

diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sql
index 2ad4f3e7387..972e3aaec49 100644
--- a/src/test/regress/sql/numeric.sql
+++ b/src/test/regress/sql/numeric.sql
@@ -798,6 +798,14 @@ SELECT '' AS to_char_34, to_char('100'::numeric, 'f"\\ool"999');
 SELECT '' AS to_char_35, to_char('100'::numeric, 'f"ool\"999');
 SELECT '' AS to_char_36, to_char('100'::numeric, 'f"ool\\"999');
 
+-- Test scientific notation with various exponents
+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;
+
 -- TO_NUMBER()
 --
 SET lc_numeric = 'C';