From 14521c7406ff0c8e3b42018df360ee2f14819094 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Branimir=20Karad=C5=BEi=C4=87?= <branimirkaradzic@gmail.com>
Date: Sun, 14 Jan 2018 19:13:34 -0800
Subject: [PATCH] Removed reliance on sinf/cosf CRT functions.

---
 include/bx/inline/math.inl | 10 ++++++
 include/bx/math.h          |  3 ++
 src/math.cpp               | 70 +++++++++++++++++++++++++++++++++-----
 tests/math_test.cpp        | 17 ++++++++-
 4 files changed, 91 insertions(+), 9 deletions(-)

diff --git a/include/bx/inline/math.inl b/include/bx/inline/math.inl
index 5167a40..710ff0b 100644
--- a/include/bx/inline/math.inl
+++ b/include/bx/inline/math.inl
@@ -122,6 +122,16 @@ namespace bx
 		return _a * _a;
 	}
 
+	inline float sin(float _a)
+	{
+		return cos(_a - kPiHalf);
+	}
+
+	inline float pow(float _a, float _b)
+	{
+		return exp(_b * log(_a) );
+	}
+
 	inline float exp2(float _a)
 	{
 		return pow(2.0f, _a);
diff --git a/include/bx/math.h b/include/bx/math.h
index 9b60134..834fbe9 100644
--- a/include/bx/math.h
+++ b/include/bx/math.h
@@ -125,6 +125,9 @@ namespace bx
 	///
 	float pow(float _a, float _b);
 
+	///
+	float exp(float _a);
+
 	///
 	float exp2(float _a);
 
diff --git a/src/math.cpp b/src/math.cpp
index d480dc7..7fe5a79 100644
--- a/src/math.cpp
+++ b/src/math.cpp
@@ -22,24 +22,78 @@ namespace bx
 	const float kHuge = HUGE_VALF;
 #endif // BX_COMPILER_MSVC
 
-	float sin(float _a)
-	{
-		return ::sinf(_a);
-	}
-
 	float asin(float _a)
 	{
 		return ::asinf(_a);
 	}
 
+	namespace
+	{
+		static const float kSinC2  = -0.16666667163372039794921875f;
+		static const float kSinC4  =  8.333347737789154052734375e-3f;
+		static const float kSinC6  = -1.9842604524455964565277099609375e-4f;
+		static const float kSinC8  =  2.760012648650445044040679931640625e-6f;
+		static const float kSinC10 = -2.50293279435709337121807038784027099609375e-8f;
+
+		static const float kCosC2  = -0.5f;
+		static const float kCosC4  =  4.166664183139801025390625e-2f;
+		static const float kCosC6  = -1.388833043165504932403564453125e-3f;
+		static const float kCosC8  =  2.47562347794882953166961669921875e-5f;
+		static const float kCosC10 = -2.59630184018533327616751194000244140625e-7f;
+
+	} // namespace
+
 	float cos(float _a)
 	{
-		return ::cosf(_a);
+		const float scaled = _a * 2.0f*kInvPi;
+		const float real   = floor(scaled);
+		const float xx     = _a - real * kPiHalf;
+		const int32_t bits = int32_t(real) & 3;
+
+		float c0, c2, c4, c6, c8, c10;
+
+		if (bits == 0
+		||  bits == 2)
+		{
+			c0  = 1.0f;
+			c2  = kCosC2;
+			c4  = kCosC4;
+			c6  = kCosC6;
+			c8  = kCosC8;
+			c10 = kCosC10;
+		}
+		else
+		{
+			c0  = xx;
+			c2  = kSinC2;
+			c4  = kSinC4;
+			c6  = kSinC6;
+			c8  = kSinC8;
+			c10 = kSinC10;
+		}
+
+		const float xsq = square(xx);
+		float result;
+		result = xsq * c10    + c8;
+		result = xsq * result + c6;
+		result = xsq * result + c4;
+		result = xsq * result + c2;
+		result = xsq * result + 1.0f;
+		result *= c0;
+
+		return bits == 1 || bits == 2
+			? -result
+			:  result
+			;
 	}
 
 	float tan(float _a)
 	{
+#if 0
+		return sin(_a) / cos(_a);
+#else
 		return ::tanf(_a);
+#endif
 	}
 
 	float acos(float _a)
@@ -52,9 +106,9 @@ namespace bx
 		return ::atan2f(_y, _x);
 	}
 
-	float pow(float _a, float _b)
+	float exp(float _a)
 	{
-		return exp(_b * log(_a) );
+		return ::expf(_a);
 	}
 
 	float log(float _a)
diff --git a/tests/math_test.cpp b/tests/math_test.cpp
index d029329..13a75b4 100644
--- a/tests/math_test.cpp
+++ b/tests/math_test.cpp
@@ -52,10 +52,25 @@ TEST_CASE("libm", "")
 	REQUIRE(bx::equal( 0.89f, bx::fract( 13.89f), 0.000001f) );
 	REQUIRE(bx::equal(-0.89f, bx::fract(-13.89f), 0.000001f) );
 
-	for (float xx = 0.0f; xx < 100.0f; xx += 0.1f)
+	for (float xx = -100.0f; xx < 100.0f; xx += 0.1f)
 	{
 		REQUIRE(bx::equal(bx::pow(1.389f, xx), ::pow(1.389f, xx), 0.00001f) );
 	}
+
+	for (float xx = -100.0f; xx < 100.0f; xx += 0.1f)
+	{
+		REQUIRE(bx::equal(bx::sin(xx), ::sin(xx), 0.00001f) );
+	}
+
+	for (float xx = -100.0f; xx < 100.0f; xx += 0.1f)
+	{
+		REQUIRE(bx::equal(bx::cos(xx), ::cos(xx), 0.00001f) );
+	}
+
+	for (float xx = -100.0f; xx < 100.0f; xx += 0.1f)
+	{
+		REQUIRE(bx::equal(bx::tan(xx), ::tan(xx), 0.00001f) );
+	}
 }
 
 TEST_CASE("ToBits", "")