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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
#ifndef INCLUDED_ORCUS_DETAIL_NUMERIC_PARSER_HPP
#define INCLUDED_ORCUS_DETAIL_NUMERIC_PARSER_HPP
#include <mdds/global.hpp>
#include <limits>
#include <cmath>
namespace orcus { namespace detail {
struct generic_parser_trait {};
struct json_parser_trait {};
struct parser_state
{
/** number of digits before the decimal point. */
int int_digit_count = 0;
/** number of digits after the decimal point. */
int frac_digit_count = 0;
/** first digit before the decimal point. */
char first_int_digit = 0;
double parsed_value = 0.0;
double divisor = 1.0;
bool has_digit = false;
bool has_decimal = false;
bool negative_sign = false;
};
template<typename _Trait>
double make_final_value(const parser_state& state);
template<>
inline double make_final_value<generic_parser_trait>(const parser_state& state)
{
return state.negative_sign ? -state.parsed_value : state.parsed_value;
}
template<>
inline double make_final_value<json_parser_trait>(const parser_state& state)
{
if (state.int_digit_count > 1 && state.first_int_digit == 0)
// leading zeros not allowed.
return std::numeric_limits<double>::quiet_NaN();
if (state.has_decimal && (state.frac_digit_count == 0 || state.int_digit_count == 0))
// at least one digit is required both before and after the decimal point.
return std::numeric_limits<double>::quiet_NaN();
return state.negative_sign ? -state.parsed_value : state.parsed_value;
}
template<typename _Trait>
class numeric_parser
{
using trait_type = _Trait;
const char* mp_char;
const char* mp_end;
parser_state m_state;
bool check_sign()
{
bool negative_sign = false;
// Check for presence of a sign.
if (mp_char != mp_end)
{
switch (*mp_char)
{
case '+':
++mp_char;
break;
case '-':
negative_sign = true;
++mp_char;
break;
default:
;
}
}
return negative_sign;
}
/**
* Parse the exponent part of a numeric string.
*
* @return extra divisor to multiply to the original divisor, or 0.0 if the
* parsing fails.
*/
double parse_exponent()
{
const char* p0 = mp_char - 1; // original position to restore to in case of parsing failure. The e needs to be added back as well.
double exponent = 0.0;
bool valid = false;
bool negative_sign = check_sign();
for (; mp_char != mp_end; ++mp_char)
{
if (*mp_char < '0' || '9' < *mp_char)
{
// Non-digit encountered.
break;
}
valid = true;
exponent *= 10.0;
exponent += *mp_char - '0';
}
if (!valid)
{
// Restore the original position on failed parsing.
mp_char = p0;
return 0.0;
}
if (!negative_sign)
exponent = -exponent;
return std::pow(10.0, exponent);
}
public:
numeric_parser(const char* p, const char* p_end) :
mp_char(p),
mp_end(p_end) {}
/**
* Start parsing the string.
*
* @return a finite value upon successful parsing, else NaN is returned.
*/
double parse()
{
m_state.negative_sign = check_sign();
for (; mp_char != mp_end; ++mp_char)
{
if (*mp_char == '.')
{
if (m_state.has_decimal)
{
// Second '.' encountered. Terminate the parsing.
m_state.parsed_value /= m_state.divisor;
return make_final_value<trait_type>(m_state);
}
m_state.has_decimal = true;
continue;
}
if (m_state.has_digit && (*mp_char == 'e' || *mp_char == 'E'))
{
++mp_char;
double extra_divisor = parse_exponent();
if (extra_divisor)
m_state.divisor *= extra_divisor;
break;
}
if (*mp_char < '0' || '9' < *mp_char)
{
if (!m_state.has_digit) // without a digit we have no numbers
return std::numeric_limits<double>::quiet_NaN();
m_state.parsed_value /= m_state.divisor;
return make_final_value<trait_type>(m_state);
}
m_state.has_digit = true;
char digit = *mp_char - '0';
if (m_state.has_decimal)
++m_state.frac_digit_count;
else
{
if (!m_state.int_digit_count)
m_state.first_int_digit = digit;
++m_state.int_digit_count;
}
m_state.parsed_value *= 10.0;
m_state.parsed_value += digit;
if (m_state.has_decimal)
m_state.divisor *= 10.0;
}
if (!m_state.has_digit) // without a digit we have no numbers
return std::numeric_limits<double>::quiet_NaN();
m_state.parsed_value /= m_state.divisor;
return make_final_value<trait_type>(m_state);
}
const char* get_char_position() const
{
return mp_char;
}
};
}} // namespace orcus::detail
#endif
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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