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39 /* -------------------------------------------------------------- */
40 /* PROLOG END TAG zYx */
41
42 #ifdef __SPU__
43 #ifndef _LOG2D2_H_
44 #define _LOG2D2_H_ 1
45
46 #include <spu_intrinsics.h>
47
48 /*
49 * FUNCTION
50 * vector double _log2d2(vector double x)
51 *
52 * DESCRIPTION
53 * The function _log2d2 computes log base 2 of the input x for each
54 * of the double word elements of x. The log2 is decomposed
55 * into two parts, log2 of the exponent and log2 of the
56 * fraction. The log2 of the fraction is approximated
57 * using a 21st order polynomial of the form:
58 *
59 * __20_
60 * \
61 * log(x) = x * (1 + \ (Ci * x^i))
62 * /
63 * /____
64 * i=0
65 *
66 * for x in the range 0-1.
67 */
68 #define LOG_C00
69 #define LOG_C01
70 #define LOG_C02
71
_log2d2(vector double vx)72 static __inline vector double _log2d2(vector double vx)
73 {
74 vec_int4 addval;
75 vec_ullong2 exp_mask = spu_splats(0x7FF0000000000000ULL);
76 vec_double2 vy, vxw;
77 vec_double2 v1 = spu_splats(1.0);
78 vec_double2 x2, x4, x8, x10, p1, p2;
79
80 /* Extract the fraction component of input by forcing
81 * its exponent so that input is in the range [1.0, 2.0)
82 * and then subtract 1.0 to force it in the range
83 * [0.0, 1.0).
84 */
85 vxw = spu_sub(spu_sel(vx, v1, exp_mask), v1);
86
87 /* Compute the log2 of the exponent as exp - 1023.
88 */
89 addval = spu_add(spu_rlmask((vec_int4)vx, -20), -1023);
90
91 /* Compute the log2 of the fractional component using a 21st
92 * order polynomial. The polynomial is evaluated in two halves
93 * to improve efficiency.
94 */
95 p1 = spu_madd(spu_splats(3.61276447184348752E-05), vxw, spu_splats(-4.16662127033480827E-04));
96 p2 = spu_madd(spu_splats(-1.43988260692073185E-01), vxw, spu_splats(1.60245637034704267E-01));
97 p1 = spu_madd(vxw, p1, spu_splats(2.28193656337578229E-03));
98 p2 = spu_madd(vxw, p2, spu_splats(-1.80329036970820794E-01));
99 p1 = spu_madd(vxw, p1, spu_splats(-7.93793829370930689E-03));
100 p2 = spu_madd(vxw, p2, spu_splats(2.06098446037376922E-01));
101 p1 = spu_madd(vxw, p1, spu_splats(1.98461565426430164E-02));
102 p2 = spu_madd(vxw, p2, spu_splats(-2.40449108727688962E-01));
103 p1 = spu_madd(vxw, p1, spu_splats(-3.84093543662501949E-02));
104 p2 = spu_madd(vxw, p2, spu_splats(2.88539004851839364E-01));
105 p1 = spu_madd(vxw, p1, spu_splats(6.08335872067172597E-02));
106 p2 = spu_madd(vxw, p2, spu_splats(-3.60673760117245982E-01));
107 p1 = spu_madd(vxw, p1, spu_splats(-8.27937055456904317E-02));
108 p2 = spu_madd(vxw, p2, spu_splats(4.80898346961226595E-01));
109 p1 = spu_madd(vxw, p1, spu_splats(1.01392360727236079E-01));
110 p2 = spu_madd(vxw, p2, spu_splats(-7.21347520444469934E-01));
111 p1 = spu_madd(vxw, p1, spu_splats(-1.16530490533844182E-01));
112 p2 = spu_madd(vxw, p2, spu_splats(0.44269504088896339E+00));
113 p1 = spu_madd(vxw, p1, spu_splats(1.30009193360025350E-01));
114
115 x2 = spu_mul(vxw, vxw);
116 x4 = spu_mul(x2, x2);
117 x8 = spu_mul(x4, x4);
118 x10 = spu_mul(x8, x2);
119
120 vy = spu_madd(spu_madd(x10, p1, p2), vxw, vxw);
121
122 /* Add the log2(exponent) and the log2(fraction) to
123 * compute the final result.
124 */
125 vy = spu_add(vy, spu_extend(spu_convtf(addval, 0)));
126
127 vxw = spu_extend(spu_convtf(addval, 20));
128
129 return(vy);
130 }
131
132 #endif /* _LOG2D2_H_ */
133 #endif /* __SPU__ */
134
