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47 lines
1.2 KiB
47 lines
1.2 KiB
12 years ago
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/*
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* Copyright 2012 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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class Exp2 {
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public:
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Exp2();
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static void init();
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// Q24 in, Q24 out
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static int32_t lookup(int32_t x);
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};
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#define EXP2_LG_N_SAMPLES 10
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#define EXP2_N_SAMPLES (1 << EXP2_LG_N_SAMPLES)
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#define EXP2_INLINE
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extern int32_t exp2tab[EXP2_N_SAMPLES << 1];
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#ifdef EXP2_INLINE
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inline
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int32_t Exp2::lookup(int32_t x) {
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const int SHIFT = 24 - EXP2_LG_N_SAMPLES;
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int lowbits = x & ((1 << SHIFT) - 1);
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int x_int = (x >> (SHIFT - 1)) & ((EXP2_N_SAMPLES - 1) << 1);
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int dy = exp2tab[x_int];
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int y0 = exp2tab[x_int + 1];
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int y = y0 + (((int64_t)dy * (int64_t)lowbits) >> SHIFT);
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return y >> (6 - (x >> 24));
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}
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#endif
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