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Alexander Barkov authored
MDEV-23415 Server crash or Assertion `dec_length <= str_length' failed in Item_func_format::val_str_ascii Problem: The crash happened in FORMAT(double, dec>=31, 'de_DE'). The patch for MDEV-23118 (commit 0041dacc) did not take into account that String::set_real() has a limit of 31 (FLOATING_POINT_DECIMALS) fractional digits. So for the range of 31..38 digits, set_real() switches to use: - my_fcvt() - decimal point notation, e.g. 1.9999999999 - my_gcvt() - scientific notation, e.g. 1e22 my_gcvt() returned a shorter string than Item_func_format::val_str_ascii() expected to get after the my_fcvt() call, so it crashed on assert. Solution: We cannot extend set_real() to use the my_fcvt() mode for the range of 31..38 fractional digits, because set_real() is used in a lot of places and such a change will break everything. Introducing String::set_fcvt() which always prints using my_fcvt() for the whole range of decimals 0..38, supported by the FORMAT() function.
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