From 74bda7e6cc4a5426e6262dc6d6c2416abe3fb0de Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=91=D1=80=D0=B0=D0=BD=D0=B8=D0=BC=D0=B8=D1=80=20=D0=9A?=
 =?UTF-8?q?=D0=B0=D1=80=D0=B0=D1=9F=D0=B8=D1=9B?=
 <branimirkaradzic@gmail.com>
Date: Tue, 30 Apr 2024 23:50:43 -0700
Subject: [PATCH] Added bx::sinCosApprox.

---
 include/bx/inline/math.inl | 14 ++++++++++++++
 include/bx/math.h          |  7 +++++++
 tests/math_test.cpp        | 30 ++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+)

diff --git a/include/bx/inline/math.inl b/include/bx/inline/math.inl
index f5b94c4..183887b 100644
--- a/include/bx/inline/math.inl
+++ b/include/bx/inline/math.inl
@@ -162,6 +162,20 @@ namespace bx
 		return _a * _a;
 	}
 
+	inline void sinCosApprox(float _a, float* _outSin, float* _outCos)
+	{
+		const float aa     = _a - floor(_a/kPi2)*kPi2;
+		const float absA   = abs(aa);
+		const float cosA   = cos(absA);
+		const float cosASq = square(cosA);
+		const float tmp0   = sqrt(1.0f - cosASq);
+		const float tmp1   = aa > 0.0f && aa < kPi ? 1.0f : -1.0f;
+		const float sinA   = mul(tmp0, tmp1);
+
+		*_outSin = sinA;
+		*_outCos = cosA;
+	}
+
 	inline BX_CONST_FUNC float sin(float _a)
 	{
 		return cos(_a - kPiHalf);
diff --git a/include/bx/math.h b/include/bx/math.h
index c6e662a..808da6f 100644
--- a/include/bx/math.h
+++ b/include/bx/math.h
@@ -203,6 +203,13 @@ namespace bx
 	///
 	BX_CONSTEXPR_FUNC float square(float _a);
 
+	/// Returns the both sine and cosine of the argument _a.
+	///
+	/// @remarks The function calculates cosine, and then approximates sine based on the cosine
+	///   result. Therefore calculation of sine is less accurate than calling `bx::sin` function.
+	///
+	void sinCosApprox(float _a, float* _outSin, float* _outCos);
+
 	/// Returns the sine of the argument _a.
 	///
 	BX_CONST_FUNC float sin(float _a);
diff --git a/tests/math_test.cpp b/tests/math_test.cpp
index c98f4ee..55b7ae7 100644
--- a/tests/math_test.cpp
+++ b/tests/math_test.cpp
@@ -441,6 +441,36 @@ TEST_CASE("sin", "[math][libm]")
 	}
 }
 
+TEST_CASE("sinCos", "[math][libm]")
+{
+	bx::WriterI* writer = bx::getNullOut();
+	bx::Error err;
+
+	for (float xx = -100.0f; xx < 100.0f; xx += 0.1f)
+	{
+		float ss, cc;
+		bx::sinCosApprox(xx, &ss, &cc);
+
+		bx::write(writer, &err, "sinCos(%f) == sin %f (expected: %f)\n", xx, ss, ::sinf(xx) );
+		bx::write(writer, &err, "sinCos(%f) == cos %f (expected: %f)\n", xx, cc, ::cosf(xx) );
+		REQUIRE(err.isOk() );
+		REQUIRE(bx::isEqual(ss, ::sinf(xx), 0.001f) );
+		REQUIRE(bx::isEqual(cc, ::cosf(xx), 0.00001f) );
+	}
+
+	for (float xx = -bx::kPi2; xx < bx::kPi2; xx += 0.0001f)
+	{
+		float ss, cc;
+		bx::sinCosApprox(xx, &ss, &cc);
+
+		bx::write(writer, &err, "sinCos(%f) == sin %f (expected: %f)\n", xx, ss, ::sinf(xx) );
+		bx::write(writer, &err, "sinCos(%f) == cos %f (expected: %f)\n", xx, cc, ::cosf(xx) );
+		REQUIRE(err.isOk() );
+		REQUIRE(bx::isEqual(ss, ::sinf(xx), 0.001f) );
+		REQUIRE(bx::isEqual(cc, ::cosf(xx), 0.00001f) );
+	}
+}
+
 TEST_CASE("sinh", "[math][libm]")
 {
 	bx::WriterI* writer = bx::getNullOut();