fix overflow check in parse_number_token

[Ramya-9353]

value{{"foo", {1, 2, 3}}}.find_pointer(
    "/foo/" + std::to_string(SIZE_MAX) + "9", ec);
// ec == error::not_found, expected error::token_overflow

parse_number_token flags std::size_t overflow with new_result < result, the
addition-overflow idiom, but the accumulation is result * 10 + d. Once
result * 10 wraps, the wrapped value plus d can land at or above result,
so a pointer token an order of magnitude past max() slips through and resolves
to a bogus (out-of-range) index, reporting error::not_found rather than
error::token_overflow. Replaced with the pre-check
result > (std::size_t(-1) - d) / 10.

The regression test appends a digit to max() and expects token_overflow; it
fails before the change and passes after. The existing overflow test only covers
max() + 1, which happens to wrap below result and so was already caught.

[cppalliance-bot]

An automated preview of the documentation is available at https://1171.json.prtest2.cppalliance.org/libs/json/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-07-17 10:18:50 UTC

[cppalliance-bot]

GCOVR code coverage report https://1171.json.prtest2.cppalliance.org/gcovr/index.html
LCOV code coverage report https://1171.json.prtest2.cppalliance.org/genhtml/index.html
Coverage Diff Report https://1171.json.prtest2.cppalliance.org/diff-report/index.html

Build time: 2026-07-17 10:32:06 UTC

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1171/pullrequest.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.91%. Comparing base (c57359d) to head (66df698).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1171   +/-   ##
========================================
  Coverage    93.91%   93.91%           
========================================
  Files           91       91           
  Lines         9265     9268    +3     
========================================
+ Hits          8701     8704    +3     
  Misses         564      564           

Files with missing lines	Coverage Δ
include/boost/json/impl/pointer.ipp	100.00% <100.00%> (ø)

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[grisumbras]

How about something like this?

if( result > UINT64_MAX / 10 )
{
    BOOST_JSON_FAIL(ec, error::token_overflow);
    return {};
}
result *= 10;

if( result > UINT64_MAX - d )
{
    BOOST_JSON_FAIL(ec, error::token_overflow);
    return {};
}
result += d;

I've checked on Godbolt and produces less code.

[Ramya-9353]

Done, pushed the two-step guard. One adjustment: result is std::size_t, so I used std::size_t(-1) as the bound rather than UINT64_MAX, which would never fire on 32-bit targets. Pointer suite still passes, 185 total, including the max()+'9' regression.

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1171/pullrequest.html