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#include <Common/intExp.h>
#include <Parsers/CommonParsers.h>
#include <Parsers/ParserSampleRatio.h>
#include <Parsers/ASTSampleRatio.h>
#include <IO/ReadHelpers.h>
namespace DB
{
static bool parseDecimal(const char * pos, const char * end, ASTSampleRatio::Rational & res)
{
UInt64 num_before = 0;
UInt64 num_after = 0;
Int32 exponent = 0;
const char * pos_after_first_num = tryReadIntText(num_before, pos, end);
bool has_num_before_point = pos_after_first_num > pos;
pos = pos_after_first_num;
bool has_point = pos < end && *pos == '.';
if (has_point)
++pos;
if (!has_num_before_point && !has_point)
return false;
int number_of_digits_after_point = 0;
if (has_point)
{
const char * pos_after_second_num = tryReadIntText(num_after, pos, end);
number_of_digits_after_point = static_cast<int>(pos_after_second_num - pos);
pos = pos_after_second_num;
}
bool has_exponent = pos < end && (*pos == 'e' || *pos == 'E');
if (has_exponent)
{
++pos;
const char * pos_after_exponent = tryReadIntText(exponent, pos, end);
if (pos_after_exponent == pos)
return false;
}
res.numerator = num_before * intExp10(number_of_digits_after_point) + num_after;
res.denominator = intExp10(number_of_digits_after_point);
if (exponent > 0)
res.numerator *= intExp10(exponent);
if (exponent < 0)
res.denominator *= intExp10(-exponent);
/// NOTE You do not need to remove the common power of ten from the numerator and denominator.
return true;
}
/** Possible options:
*
* 12345
* - an integer
*
* 0.12345
* .12345
* 0.
* - fraction in ordinary decimal notation
*
* 1.23e-1
* - fraction in scientific decimal notation
*
* 123 / 456
* - fraction with an ordinary denominator
*
* Just in case, in the numerator and denominator of the fraction, we support the previous cases.
* Example:
* 123.0 / 456e0
*/
bool ParserSampleRatio::parseImpl(Pos & pos, ASTPtr & node, Expected &)
{
ASTSampleRatio::Rational numerator;
ASTSampleRatio::Rational denominator;
ASTSampleRatio::Rational res;
if (!parseDecimal(pos->begin, pos->end, numerator))
return false;
++pos;
bool has_slash = pos->type == TokenType::Slash;
if (has_slash)
{
++pos;
if (!parseDecimal(pos->begin, pos->end, denominator))
return false;
++pos;
res.numerator = numerator.numerator * denominator.denominator;
res.denominator = numerator.denominator * denominator.numerator;
}
else
{
res = numerator;
}
node = std::make_shared<ASTSampleRatio>(res);
return true;
}
}
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