[Beignet] [PATCH] backend: add double version of atan

[rander]

	cp from fdlibm and pass the cft after refined

Signed-off-by: rander <rander.wang at intel.com>
---
 backend/src/libocl/tmpl/ocl_math_common.tmpl.cl | 75 +++++++++++++++++++++++++
 backend/src/libocl/tmpl/ocl_math_common.tmpl.h  |  1 +
 2 files changed, 76 insertions(+)

diff --git a/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl b/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
index e655955..d6ee279 100644
--- a/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
+++ b/backend/src/libocl/tmpl/ocl_math_common.tmpl.cl
@@ -236,6 +236,81 @@ OVERLOADABLE double asinh(double x)
 	if(hx>0) return w; else return -w;
 }
 
+OVERLOADABLE double atan(double x)
+{
+	double atanhi[] = {
+	  4.63647609000806093515e-01, /* atan(0.5)hi 0x3FDDAC67, 0x0561BB4F */
+	  7.85398163397448278999e-01, /* atan(1.0)hi 0x3FE921FB, 0x54442D18 */
+	  9.82793723247329054082e-01, /* atan(1.5)hi 0x3FEF730B, 0xD281F69B */
+	  1.57079632679489655800e+00, /* atan(inf)hi 0x3FF921FB, 0x54442D18 */
+	};
+
+	double atanlo[] = {
+	  2.26987774529616870924e-17, /* atan(0.5)lo 0x3C7A2B7F, 0x222F65E2 */
+	  3.06161699786838301793e-17, /* atan(1.0)lo 0x3C81A626, 0x33145C07 */
+	  1.39033110312309984516e-17, /* atan(1.5)lo 0x3C700788, 0x7AF0CBBD */
+	  6.12323399573676603587e-17, /* atan(inf)lo 0x3C91A626, 0x33145C07 */
+	};
+
+	double aT[] = {
+	  3.33333333333329318027e-01, /* 0x3FD55555, 0x5555550D */
+	 -1.99999999998764832476e-01, /* 0xBFC99999, 0x9998EBC4 */
+	  1.42857142725034663711e-01, /* 0x3FC24924, 0x920083FF */
+	 -1.11111104054623557880e-01, /* 0xBFBC71C6, 0xFE231671 */
+	  9.09088713343650656196e-02, /* 0x3FB745CD, 0xC54C206E */
+	 -7.69187620504482999495e-02, /* 0xBFB3B0F2, 0xAF749A6D */
+	  6.66107313738753120669e-02, /* 0x3FB10D66, 0xA0D03D51 */
+	 -5.83357013379057348645e-02, /* 0xBFADDE2D, 0x52DEFD9A */
+	  4.97687799461593236017e-02, /* 0x3FA97B4B, 0x24760DEB */
+	 -3.65315727442169155270e-02, /* 0xBFA2B444, 0x2C6A6C2F */
+	  1.62858201153657823623e-02, /* 0x3F90AD3A, 0xE322DA11 */
+	};
+
+	double one   = 1.0,
+	huge   = 1.0e300;
+	double w,s1,s2,z;
+	int ix,hx,id;
+
+	hx = __HI(x);
+	ix = hx&0x7fffffff;
+	if(ix>=0x44100000) {	/* if |x| >= 2^66 */
+		if(ix>0x7ff00000 ||(ix==0x7ff00000 && (__LO(x)!=0)))
+		return x+x;		/* NaN */
+		if(hx>0) return  atanhi[3]+atanlo[3];
+		else	 return -atanhi[3]-atanlo[3];
+	} if (ix < 0x3fdc0000) {	/* |x| < 0.4375 */
+		if (ix < 0x3e200000) {	/* |x| < 2^-29 */
+		if(huge+x>one) return x;	/* raise inexact */
+		}
+		id = -1;
+	} else {
+	x = fabs(x);
+	if (ix < 0x3ff30000) {		/* |x| < 1.1875 */
+		if (ix < 0x3fe60000) {	/* 7/16 <=|x|<11/16 */
+		id = 0; x = (2.0*x-one)/(2.0+x);
+		} else {			/* 11/16<=|x|< 19/16 */
+		id = 1; x  = (x-one)/(x+one);
+		}
+	} else {
+		if (ix < 0x40038000) {	/* |x| < 2.4375 */
+		id = 2; x  = (x-1.5)/(one+1.5*x);
+		} else {			/* 2.4375 <= |x| < 2^66 */
+		id = 3; x  = -1.0/x;
+		}
+	}}
+	/* end of argument reduction */
+	z = x*x;
+	w = z*z;
+	/* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
+	s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
+	s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
+	if (id<0) return x - x*(s1+s2);
+	else {
+		z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
+		return (hx<0)? -z:z;
+	}
+}
+
 OVERLOADABLE double ceil(double x)
 {
     double ret;
diff --git a/backend/src/libocl/tmpl/ocl_math_common.tmpl.h b/backend/src/libocl/tmpl/ocl_math_common.tmpl.h
index 56c9787..46dc788 100644
--- a/backend/src/libocl/tmpl/ocl_math_common.tmpl.h
+++ b/backend/src/libocl/tmpl/ocl_math_common.tmpl.h
@@ -26,6 +26,7 @@ OVERLOADABLE double acosh(double x);
 OVERLOADABLE double asin(double x);
 OVERLOADABLE double asinpi(double x);
 OVERLOADABLE double asinh(double x);
+OVERLOADABLE double atan(double x);
 OVERLOADABLE double ceil(double x);
 OVERLOADABLE double copysign(double x, double y);
 OVERLOADABLE double fabs(double x);
-- 
2.7.4