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Test the overflow check of json_view at the largest double

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Numbers of more than 19 digits at the boundary of the largest double are
decided by the exact comparison with the midpoint in the overflow check.
The check uses the floating-point type of the document: with float, the
view rejects what parse() rejects (1e39, 3.4028236e38, the midpoint between
the largest float and 2^128), and double documents are not affected.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-30 20:19:13 +02:00
committed by GitHub
parent 9b0b4ff26d
commit 118af5015e
1 changed files with 43 additions and 0 deletions
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tests/src/unit-json_view_builder.cpp
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@@ -14,6 +14,7 @@ using nlohmann::json;
#include <cstdint>
#include <fstream>
#include <map>
#include <memory>
#include <random>
#include <sstream>
@@ -228,6 +229,48 @@ TEST_CASE("json_view builder")
{
check_same(text);
}
// the midpoint between the largest double and 2^1024 rounds to
// infinity (an overflow), one less to the largest double: with more
// than 19 digits, Eisel-Lemire cannot decide these, and the overflow
// check needs the exact comparison with the midpoint
const std::string midpoint = "179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497792";
const std::string below = "179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497791";
check_same(midpoint);
check_same("-" + midpoint);
check_same(below);
check_same("[" + below + "," + midpoint + "]");
// the check uses the floating-point type of the document: with float,
// the view rejects what parse() rejects (out_of_range.406), and a
// double document is not affected
using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
CHECK_FALSE(float_json::accept("1e39"));
CHECK(float_json::accept("3.4028235e38"));
CHECK_FALSE(float_json::accept("3.4028236e38"));
for (const char* text :
{
"1e39", "-1e39", "3.4028235e38", "-3.4028235e38", "3.4028236e38", "-3.4028236e38", "3.4028234663852886e38", "1e38",
"340282356779733661637539395458142568448", "340282356779733661637539395458142568447.99", "0.00034028236e42",
"[1.5e38, 3.5e38]", "{\"a\": 1e-50, \"b\": 1e39}"
})
{
CAPTURE(text);
const bool float_accepted = float_json::accept(text);
for (const bool sentinel :
{
true, false
})
{
const built f = build<float>(text, false, false, sentinel);
CHECK(f.ok == float_accepted);
if (!f.ok)
{
CHECK(f.failure.code == nlohmann::detail::view::error_code::number_overflow);
}
CHECK(build<double>(text, false, false, sentinel).ok == json::accept(text));
}
}
}
SECTION("malformed input")