Re: [Boost-users] [Spirit Qi] Failed to parse the following fixed format double

19 Jan 2019


      On Sat, Jan 19, 2019 at 5:05 PM Michael Powell  wrote:
...
Hello,
We've been here before, but it is still a problem. I formatted this
one using Boost.Format, "%1$.20f", especially dealing with 64-bit
floating point values:
"-6454866677007257221799838306103363329054216765979693126687924767750184064408021645577150612734391912932504859271476290909819606665305867922002041825515395649967939044362235953753132737391831714484437364695236622971838510661738713863719312223765488747173369566663518205119012003640541309414736378162701139968.00000000000000000000"
A couple more examples of failing fixed point formatted double
precision floating point values:

"-2933203577849518722807582107921270303789124551628326833223026840288067720552584469718398734780494285760864383284291153435811556533627851666237668018198306411496865670893213895174427232870273854485740801234157498001928584582425137432930105057443647782995234273328228331519807104430353167966879393151302238208.00000000000000000000"

"-5575142993783585741080266667491263474365065567007147941126088591468810775271255177205047484910285258069829661948007476427372671344939243513169304773270960157491924753398062656733759664894978353176430823579581454223501775356229158988642579674006981268033954414994235729789365374969339689104743045516916424704.00000000000000000000"

"-10961106826538223321566456661622697491480936313401307083286539463405800627473400980352364856687771070172100174159400050681199843366266743862457103239362125692763404716870083938982037356857637487843703963982090861987853380143680798438559722884237142834679878087134795785244216620052002403762015568006217728.00000000000000000000"
...
Grammar is defined:
numeric_sign %= (
    ('-' >> attr(numeric_sign_minus))
    | ('+' >> attr(numeric_sign_plus))
    )
    ;
float_lit %= real_parser>{};
floating_point %= -numeric_sign >> float_lit;
With rules defined as:
qi::rule numeric_sign;
qi::rule float_lit;
qi::rule floating_point;
Where float_t is a defined part of the AST:
using float_t = double;
And floating_point maps to the floating_point_number_t, basically
mapping the Sign and Value.
Seems like we've been here before with inadequate response, however,
reading the Boost documentation, I do not see any reason any Qi should
be rejecting this value:
https://www.boost.org/doc/libs/1_69_0/libs/spirit/doc/html/spirit/qi/referen...
Particularly the RealPolicies:
sign
    =   lit('+') | '-'
    ;
nan
    =   -lit("1.0#") >> no_case["nan"]
        >> -('(' >> *(char_ - ')') >> ')')
    ;
inf
    =   no_case[lit("inf") >> -lit("inity")]
    ;
floating_literal
    =   -sign >>
        (       nan
            |   inf
            |   fractional_constant >> -exponent_part
            |  +digit >> exponent_part
        )
    ;
fractional_constant
    =  *digit >> '.' >> +digit
    |  +digit >> -lit('.')
    ;
exponent_part
    =   (lit('e') | 'E') >> -sign >> +digit
    ;
Although the concern I have is that the RealPolicy grammar defined
above is not implemented as Qi Rules, per se, but rather brute force.
In other words, error prone in the ways that a brute force approach is
error prone.
Best regards,
Michael Powell