From a19d71ddcb891602606aa4a768fb76a2cf729b1d Mon Sep 17 00:00:00 2001
From: dhmemi <dhmemi@gmail.com>
Date: Thu, 14 Sep 2023 11:08:38 +0800
Subject: [PATCH] fix: validate multipleOf fails on float-point value

---
 .gitignore             |  1 +
 src/json-validator.cpp | 10 +++++++---
 test/CMakeLists.txt    |  4 ++++
 test/issue-293.cpp     | 27 +++++++++++++++++++++++++++
 4 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 test/issue-293.cpp

diff --git a/.gitignore b/.gitignore
index aceaf81..bc9dd9f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,4 @@ cmake-build-*
 venv
 env
 compile_commands.json
+.vs/*
diff --git a/src/json-validator.cpp b/src/json-validator.cpp
index 77d701f..2021471 100644
--- a/src/json-validator.cpp
+++ b/src/json-validator.cpp
@@ -863,9 +863,13 @@ class numeric : public schema
 	// multipleOf - if the remainder of the division is 0 -> OK
 	bool violates_multiple_of(T x) const
 	{
-		double res = std::remainder(x, multipleOf_.second);
-		double eps = std::nextafter(x, 0) - static_cast<double>(x);
-		return std::fabs(res) > std::fabs(eps);
+		if constexpr (std::is_floating_point_v<T>) {
+			auto multiple = x / multipleOf_.second;
+			auto error = std::abs((multiple - std::round(multiple)) * multipleOf_.second);
+			return error > std::numeric_limits<T>::epsilon();
+		} else {
+			return x % static_cast<T>(multipleOf_.second) != 0;
+		}
 	}
 
 	void validate(const json::json_pointer &ptr, const json &instance, json_patch &, error_handler &e) const override
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 0345b34..b461df6 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -43,6 +43,10 @@ add_executable(issue-98 issue-98.cpp)
 target_link_libraries(issue-98 nlohmann_json_schema_validator)
 add_test(NAME issue-98-erase-exception-unknown-keywords COMMAND issue-98)
 
+add_executable(issue-293 issue-293.cpp)
+target_link_libraries(issue-293 nlohmann_json_schema_validator)
+add_test(NAME issue-293-float-point-error COMMAND issue-293)
+
 # Unit test for string format checks
 add_executable(string-format-check-test string-format-check-test.cpp)
 target_include_directories(string-format-check-test PRIVATE ${PROJECT_SOURCE_DIR}/src/)
diff --git a/test/issue-293.cpp b/test/issue-293.cpp
new file mode 100644
index 0000000..fb566e1
--- /dev/null
+++ b/test/issue-293.cpp
@@ -0,0 +1,27 @@
+#include "nlohmann/json-schema.hpp"
+
+int main(void)
+{
+	using nlohmann::json_schema::json_validator;
+
+	json_validator({{"type", "number"}, {"multipleOf", 0.001}}).validate(0.3 - 0.2);
+
+	json_validator({{"type", "number"}, {"multipleOf", 3.3}}).validate(8.0 - 1.4);
+
+	json_validator({{"type", "number"}, {"multipleOf", 1000.01}}).validate((1000.03 - 0.02) * 15.0);
+
+	int expect_exception = 2;
+	try {
+		json_validator({{"type", "number"}, {"multipleOf", 0.001}}).validate(0.3 - 0.2005);
+	} catch (const std::exception &ex) {
+		expect_exception--;
+	}
+
+	try {
+		json_validator({{"type", "number"}, {"multipleOf", 1000.02}}).validate((1000.03 - 0.02) * 15.0);
+	} catch (const std::exception &ex) {
+		expect_exception--;
+	}
+
+	return expect_exception;
+}