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117 lines
2.7 KiB
C++
117 lines
2.7 KiB
C++
#include <Common/intExp.h>
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#include <Parsers/CommonParsers.h>
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#include <Parsers/ParserSampleRatio.h>
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#include <Parsers/ASTSampleRatio.h>
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#include <IO/ReadHelpers.h>
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namespace DB
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{
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static bool parseDecimal(const char * pos, const char * end, ASTSampleRatio::Rational & res)
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{
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UInt64 num_before = 0;
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UInt64 num_after = 0;
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Int64 exponent = 0;
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const char * pos_after_first_num = tryReadIntText(num_before, pos, end);
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bool has_num_before_point = pos_after_first_num > pos;
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pos = pos_after_first_num;
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bool has_point = pos < end && *pos == '.';
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if (has_point)
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++pos;
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if (!has_num_before_point && !has_point)
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return false;
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size_t number_of_digits_after_point = 0;
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if (has_point)
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{
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const char * pos_after_second_num = tryReadIntText(num_after, pos, end);
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number_of_digits_after_point = pos_after_second_num - pos;
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pos = pos_after_second_num;
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}
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bool has_exponent = pos < end && (*pos == 'e' || *pos == 'E');
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if (has_exponent)
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{
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++pos;
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const char * pos_after_exponent = tryReadIntText(exponent, pos, end);
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if (pos_after_exponent == pos)
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return false;
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}
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res.numerator = num_before * intExp10(number_of_digits_after_point) + num_after;
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res.denominator = intExp10(number_of_digits_after_point);
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if (exponent > 0)
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res.numerator *= intExp10(exponent);
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if (exponent < 0)
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res.denominator *= intExp10(-exponent);
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/// NOTE You do not need to remove the common power of ten from the numerator and denominator.
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return true;
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}
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/** Possible options:
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*
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* 12345
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* - an integer
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*
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* 0.12345
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* .12345
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* 0.
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* - fraction in ordinary decimal notation
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*
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* 1.23e-1
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* - fraction in scientific decimal notation
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*
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* 123 / 456
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* - fraction with an ordinary denominator
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*
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* Just in case, in the numerator and denominator of the fraction, we support the previous cases.
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* Example:
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* 123.0 / 456e0
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*/
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bool ParserSampleRatio::parseImpl(Pos & pos, ASTPtr & node, Expected &)
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{
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ASTSampleRatio::Rational numerator;
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ASTSampleRatio::Rational denominator;
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ASTSampleRatio::Rational res;
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if (!parseDecimal(pos->begin, pos->end, numerator))
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return false;
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++pos;
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bool has_slash = pos->type == TokenType::Slash;
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if (has_slash)
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{
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++pos;
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if (!parseDecimal(pos->begin, pos->end, denominator))
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return false;
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++pos;
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res.numerator = numerator.numerator * denominator.denominator;
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res.denominator = numerator.denominator * denominator.numerator;
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}
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else
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{
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res = numerator;
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}
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node = std::make_shared<ASTSampleRatio>(res);
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return true;
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}
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}
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