From d07a55a852e3e9430daba9068878b1ac10605f0a Mon Sep 17 00:00:00 2001
From: Merry <8682882+merryhime@users.noreply.github.com>
Date: Fri, 29 Mar 2024 20:53:26 +0000
Subject: [PATCH] cxxrtl: Fix sdivmod

x = x.neg(); results in the subsequent x.is_neg() always being false.
Ditto for the dividend.is_neg() != divisor.is_neg() test.
---
 backends/cxxrtl/runtime/cxxrtl/cxxrtl.h |   8 +-
 tests/cxxrtl/test_value_fuzz.cc         | 105 ++++++++++++++++++++++++
 2 files changed, 109 insertions(+), 4 deletions(-)

diff --git a/backends/cxxrtl/runtime/cxxrtl/cxxrtl.h b/backends/cxxrtl/runtime/cxxrtl/cxxrtl.h
index b834cd12019..16aa900f1a5 100644
--- a/backends/cxxrtl/runtime/cxxrtl/cxxrtl.h
+++ b/backends/cxxrtl/runtime/cxxrtl/cxxrtl.h
@@ -625,11 +625,11 @@ struct value : public expr_base<value<Bits>> {
 		value<Bits + 1> remainder;
 		value<Bits + 1> dividend = sext<Bits + 1>();
 		value<Bits + 1> divisor = other.template sext<Bits + 1>();
-		if (dividend.is_neg()) dividend = dividend.neg();
-		if (divisor.is_neg()) divisor = divisor.neg();
+		if (is_neg()) dividend = dividend.neg();
+		if (other.is_neg()) divisor = divisor.neg();
 		std::tie(quotient, remainder) = dividend.udivmod(divisor);
-		if (dividend.is_neg() != divisor.is_neg()) quotient = quotient.neg();
-		if (dividend.is_neg()) remainder = remainder.neg();
+		if (is_neg() != other.is_neg()) quotient = quotient.neg();
+		if (is_neg()) remainder = remainder.neg();
 		return {quotient.template trunc<Bits>(), remainder.template trunc<Bits>()};
 	}
 };
diff --git a/tests/cxxrtl/test_value_fuzz.cc b/tests/cxxrtl/test_value_fuzz.cc
index 4428e9f6e7f..a7bbb293afc 100644
--- a/tests/cxxrtl/test_value_fuzz.cc
+++ b/tests/cxxrtl/test_value_fuzz.cc
@@ -25,6 +25,11 @@ T rand_int(T min = std::numeric_limits<T>::min(), T max = std::numeric_limits<T>
 	return dist(generator);
 }
 
+int64_t sext(size_t bits, uint64_t value)
+{
+	return (int64_t)(value << (64 - bits)) >> (64 - bits);
+}
+
 struct BinaryOperationBase
 {
 	void tweak_input(uint64_t &a, uint64_t &b) {}
@@ -246,6 +251,106 @@ struct CtlzTest
 	}
 } ctlz;
 
+struct UdivTest : BinaryOperationBase
+{
+	UdivTest()
+	{
+		std::printf("Randomized tests for value::udivmod (div):\n");
+		test_binary_operation(*this);
+	}
+
+	uint64_t reference_impl(size_t bits, uint64_t a, uint64_t b)
+	{
+		return a / b;
+	}
+
+	template<size_t Bits>
+	cxxrtl::value<Bits> testing_impl(cxxrtl::value<Bits> a, cxxrtl::value<Bits> b)
+	{
+		return std::get<0>(a.udivmod(b));
+	}
+
+	void tweak_input(uint64_t &, uint64_t &b)
+	{
+		if (b == 0) b = 1; // Avoid divide by zero
+	}
+} udiv;
+
+struct UmodTest : BinaryOperationBase
+{
+	UmodTest()
+	{
+		std::printf("Randomized tests for value::udivmod (mod):\n");
+		test_binary_operation(*this);
+	}
+
+	uint64_t reference_impl(size_t bits, uint64_t a, uint64_t b)
+	{
+		return a % b;
+	}
+
+	template<size_t Bits>
+	cxxrtl::value<Bits> testing_impl(cxxrtl::value<Bits> a, cxxrtl::value<Bits> b)
+	{
+		return std::get<1>(a.udivmod(b));
+	}
+
+	void tweak_input(uint64_t &, uint64_t &b)
+	{
+		if (b == 0) b = 1; // Avoid divide by zero
+	}
+} umod;
+
+struct SdivTest : BinaryOperationBase
+{
+	SdivTest()
+	{
+		std::printf("Randomized tests for value::sdivmod (div):\n");
+		test_binary_operation(*this);
+	}
+
+	uint64_t reference_impl(size_t bits, uint64_t a, uint64_t b)
+	{
+		return (uint64_t)(sext(bits, a) / sext(bits, b));
+	}
+
+	template<size_t Bits>
+	cxxrtl::value<Bits> testing_impl(cxxrtl::value<Bits> a, cxxrtl::value<Bits> b)
+	{
+		return std::get<0>(a.sdivmod(b));
+	}
+
+	void tweak_input(uint64_t &, uint64_t &b)
+	{
+		if (b == 0) b = 1; // Avoid divide by zero
+	}
+} sdiv;
+
+struct SmodTest : BinaryOperationBase
+{
+	SmodTest()
+	{
+		std::printf("Randomized tests for value::sdivmod (mod):\n");
+		test_binary_operation(*this);
+	}
+
+	uint64_t reference_impl(size_t bits, uint64_t a, uint64_t b)
+	{
+		return (uint64_t)(sext(bits, a) % sext(bits, b));
+	}
+
+	template<size_t Bits>
+	cxxrtl::value<Bits> testing_impl(cxxrtl::value<Bits> a, cxxrtl::value<Bits> b)
+	{
+		return std::get<1>(a.sdivmod(b));
+	}
+
+	void tweak_input(uint64_t &, uint64_t &b)
+	{
+		if (b == 0) b = 1; // Avoid divide by zero
+	}
+} smod;
+
 int main()
 {
 }