40c7fcbbed
This makes the choice of result scale of numeric power() for integer exponents consistent with the choice for non-integer exponents, and with the result scale of other numeric functions. Specifically, the result scale will be at least as large as the scale of either input, and sufficient to ensure that the result has at least 16 significant digits. Formerly, the result scale was based only on the scale of the first input, without taking into account the weight of the result. For results with negative weight, that could lead to results with very few or even no non-zero significant digits (e.g., 10.0 ^ (-18) produced 0.0000000000000000). Fix this by moving responsibility for the choice of result scale into power_var_int(), which already has code to estimate the result weight. Per report by Adrian Klaver and suggested fix by Tom Lane. No back-patch -- arguably this is a bug fix, but one which is easy to work around, so it doesn't seem worth the risk of changing query results in stable branches. Discussion: https://postgr.es/m/12a40226-70ac-3a3b-3d3a-fdaf9e32d312%40aklaver.com
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