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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef _LIBS_UTILS_LINEAR_TRANSFORM_H
#define _LIBS_UTILS_LINEAR_TRANSFORM_H
#include <stdint.h>
namespace android {
// LinearTransform defines a structure which hold the definition of a
// transformation from single dimensional coordinate system A into coordinate
// system B (and back again). Values in A and in B are 64 bit, the linear
// scale factor is expressed as a rational number using two 32 bit values.
//
// Specifically, let
// f(a) = b
// F(b) = f^-1(b) = a
// then
//
// f(a) = (((a - a_zero) * a_to_b_numer) / a_to_b_denom) + b_zero;
//
// and
//
// F(b) = (((b - b_zero) * a_to_b_denom) / a_to_b_numer) + a_zero;
//
struct LinearTransform {
int64_t a_zero;
int64_t b_zero;
int32_t a_to_b_numer;
uint32_t a_to_b_denom;
// Transform from A->B
// Returns true on success, or false in the case of a singularity or an
// overflow.
bool doForwardTransform(int64_t a_in, int64_t* b_out) const;
// Transform from B->A
// Returns true on success, or false in the case of a singularity or an
// overflow.
bool doReverseTransform(int64_t b_in, int64_t* a_out) const;
// Helpers which will reduce the fraction N/D using Euclid's method.
template <class T> static void reduce(T* N, T* D);
static void reduce(int32_t* N, uint32_t* D);
};
}
#endif // _LIBS_UTILS_LINEAR_TRANSFORM_H
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