1 /* -------------------------------------------------------------- */
2 /* (C)Copyright 2001,2008, */
3 /* International Business Machines Corporation, */
4 /* Sony Computer Entertainment, Incorporated, */
5 /* Toshiba Corporation, */
6 /* */
7 /* All Rights Reserved. */
8 /* */
9 /* Redistribution and use in source and binary forms, with or */
10 /* without modification, are permitted provided that the */
11 /* following conditions are met: */
12 /* */
13 /* - Redistributions of source code must retain the above copyright*/
14 /* notice, this list of conditions and the following disclaimer. */
15 /* */
16 /* - Redistributions in binary form must reproduce the above */
17 /* copyright notice, this list of conditions and the following */
18 /* disclaimer in the documentation and/or other materials */
19 /* provided with the distribution. */
20 /* */
21 /* - Neither the name of IBM Corporation nor the names of its */
22 /* contributors may be used to endorse or promote products */
23 /* derived from this software without specific prior written */
24 /* permission. */
25 /* */
26 /* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND */
27 /* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, */
28 /* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF */
29 /* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE */
30 /* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR */
31 /* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, */
32 /* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT */
33 /* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; */
34 /* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) */
35 /* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN */
36 /* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR */
37 /* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, */
38 /* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
39 /* -------------------------------------------------------------- */
40 /* PROLOG END TAG zYx */
41 #ifdef __SPU__
42
43 #ifndef _LOG2F4_H_
44 #define _LOG2F4_H_ 1
45
46 #include <spu_intrinsics.h>
47
48 /*
49 * FUNCTION
50 * vector float _log2f4(vector float x)
51 *
52 * DESCRIPTION
53 * The _log2f4 function computes log (base 2) on a vector if inputs
54 * values x. The _log2f4 function is approximated as a polynomial of
55 * order 8 (C. Hastings, Jr, 1955).
56 *
57 * __8__
58 * \
59 * \
60 * log2f(1+x) = / Ci*x^i
61 * /____
62 * i=1
63 *
64 * for x in the range 0.0 to 1.0
65 *
66 * C1 = 1.4426898816672
67 * C2 = -0.72116591947498
68 * C3 = 0.47868480909345
69 * C4 = -0.34730547155299
70 * C5 = 0.24187369696082
71 * C6 = -0.13753123777116
72 * C7 = 0.052064690894143
73 * C8 = -0.0093104962134977
74 *
75 * This function assumes that x is a non-zero positive value.
76 *
77 */
_log2f4(vector float x)78 static __inline vector float _log2f4(vector float x)
79 {
80 vector signed int exponent;
81 vector float result;
82 vector float x2, x4;
83 vector float hi, lo;
84
85 /* Extract the exponent from the input X.
86 */
87 exponent = (vector signed int)spu_and(spu_rlmask((vector unsigned int)(x), -23), 0xFF);
88 exponent = spu_add(exponent, -127);
89
90 /* Compute the remainder after removing the exponent.
91 */
92 x = (vector float)spu_sub((vector signed int)(x), spu_sl(exponent, 23));
93
94 /* Calculate the log2 of the remainder using the polynomial
95 * approximation.
96 */
97 x = spu_sub(x, spu_splats(1.0f));
98
99 /* Instruction counts can be reduced if the polynomial was
100 * computed entirely from nested (dependent) fma's. However,
101 * to reduce the number of pipeline stalls, the polygon is evaluated
102 * in two halves (hi amd lo).
103 */
104 x2 = spu_mul(x, x);
105 x4 = spu_mul(x2, x2);
106
107 hi = spu_madd(x, spu_splats(-0.0093104962134977f), spu_splats(0.052064690894143f));
108 hi = spu_madd(x, hi, spu_splats(-0.13753123777116f));
109 hi = spu_madd(x, hi, spu_splats( 0.24187369696082f));
110 hi = spu_madd(x, hi, spu_splats(-0.34730547155299f));
111 lo = spu_madd(x, spu_splats(0.47868480909345f), spu_splats(-0.72116591947498f));
112 lo = spu_madd(x, lo, spu_splats(1.4426898816672f));
113 lo = spu_mul(x, lo);
114 result = spu_madd(x4, hi, lo);
115
116 /* Add the exponent back into the result.
117 */
118 result = spu_add(result, spu_convtf(exponent, 0));
119
120 return (result);
121 }
122
123 #endif /* _LOG2F4_H_ */
124 #endif /* __SPU__ */
125
