65 lines
1.9 KiB
C++
65 lines
1.9 KiB
C++
/*
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* Copyright (C) 2011 The Android Open Source Project
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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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#ifndef _LIBS_UTILS_LINEAR_TRANSFORM_H
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#define _LIBS_UTILS_LINEAR_TRANSFORM_H
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#include <stdint.h>
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namespace android {
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// LinearTransform defines a structure which hold the definition of a
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// transformation from single dimensional coordinate system A into coordinate
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// system B (and back again). Values in A and in B are 64 bit, the linear
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// scale factor is expressed as a rational number using two 32 bit values.
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//
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// Specifically, let
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// f(a) = b
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// F(b) = f^-1(b) = a
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// then
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//
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// f(a) = (((a - a_zero) * a_to_b_numer) / a_to_b_denom) + b_zero;
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//
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// and
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//
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// F(b) = (((b - b_zero) * a_to_b_denom) / a_to_b_numer) + a_zero;
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//
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struct LinearTransform {
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int64_t a_zero;
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int64_t b_zero;
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int32_t a_to_b_numer;
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uint32_t a_to_b_denom;
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// Transform from A->B
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// Returns true on success, or false in the case of a singularity or an
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// overflow.
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bool doForwardTransform(int64_t a_in, int64_t* b_out) const;
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// Transform from B->A
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// Returns true on success, or false in the case of a singularity or an
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// overflow.
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bool doReverseTransform(int64_t b_in, int64_t* a_out) const;
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// Helpers which will reduce the fraction N/D using Euclid's method.
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template <class T> static void reduce(T* N, T* D);
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static void reduce(int32_t* N, uint32_t* D);
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};
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}
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#endif // _LIBS_UTILS_LINEAR_TRANSFORM_H
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