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44 lines
1.4 KiB
C++
44 lines
1.4 KiB
C++
// Copyright 2016 The Draco Authors.
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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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// File provides shared functions for adaptive rANS bit coding.
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#ifndef DRACO_CORE_ADAPTIVE_RANS_BIT_CODING_SHARED_H_
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#define DRACO_CORE_ADAPTIVE_RANS_BIT_CODING_SHARED_H_
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#include "core/macros.h"
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namespace draco {
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// Clamp the probability p to a uint8_t in the range [1,255].
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inline uint8_t clamp_probability(double p) {
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DCHECK_LE(p, 1.0);
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DCHECK_LE(0.0, p);
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uint32_t p_int = static_cast<uint32_t>((p * 256) + 0.5);
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p_int -= (p_int == 256);
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p_int += (p_int == 0);
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return static_cast<uint8_t>(p_int);
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}
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// Update the probability according to new incoming bit.
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inline double update_probability(double old_p, bool bit) {
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static constexpr double w = 128.0;
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static constexpr double w0 = (w - 1.0) / w;
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static constexpr double w1 = 1.0 / w;
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return old_p * w0 + (!bit) * w1;
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}
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} // namespace draco
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#endif // DRACO_CORE_ADAPTIVE_RANS_BIT_CODING_SHARED_H_
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