Fix conversion of exactly representable double -2^63 to int64_t

[Tyagiquamar]

Fixes #1209. The lower-bound helper for signed 64-bit integer conversion returned the next double above INT64_MIN, rejecting the exact minimum. Return the exact minimum value.

[cppalliance-bot]

An automated preview of the documentation is available at https://1210.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.

2026-10-12 12:58:56 UTC

[cppalliance-bot]

GCOVR code coverage report https://1210.json.prtest2.cppalliance.org/gcovr/index.html
LCOV code coverage report https://1210.json.prtest2.cppalliance.org/genhtml/index.html
Coverage Diff Report https://1210.json.prtest2.cppalliance.org/diff-report/index.html

Build time: 2026-10-12 13:17:31 UTC

[cppalliance-bot]

GCOVR code coverage report https://1210.json.prtest2.cppalliance.org/gcovr/index.html
LCOV code coverage report https://1210.json.prtest2.cppalliance.org/genhtml/index.html
Coverage Diff Report https://1210.json.prtest2.cppalliance.org/diff-report/index.html

Build time: 2026-10-12 13:20:17 UTC

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1210/pullrequest.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.98%. Comparing base (87c2e5e) to head (abfaa4f).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1210   +/-   ##
========================================
  Coverage    93.98%   93.98%           
========================================
  Files           85       85           
  Lines         8971     8971           
========================================
  Hits          8431     8431           
  Misses         540      540           

Files with missing lines	Coverage Δ
include/boost/json/detail/value.hpp	98.46% <100.00%> (ø)

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[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1210/pullrequest.html

[grisumbras]

Thanks for the fix. In addition to the fix I need a test that fails with current state of the project but would pass with this change.