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      1 /*
      2  * Copyright (C) 2011 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef _LIBS_UTILS_LINEAR_TRANSFORM_H
     18 #define _LIBS_UTILS_LINEAR_TRANSFORM_H
     19 
     20 #include <stdint.h>
     21 
     22 namespace android {
     23 
     24 // LinearTransform defines a structure which hold the definition of a
     25 // transformation from single dimensional coordinate system A into coordinate
     26 // system B (and back again).  Values in A and in B are 64 bit, the linear
     27 // scale factor is expressed as a rational number using two 32 bit values.
     28 //
     29 // Specifically, let
     30 // f(a) = b
     31 // F(b) = f^-1(b) = a
     32 // then
     33 //
     34 // f(a) = (((a - a_zero) * a_to_b_numer) / a_to_b_denom) + b_zero;
     35 //
     36 // and
     37 //
     38 // F(b) = (((b - b_zero) * a_to_b_denom) / a_to_b_numer) + a_zero;
     39 //
     40 struct LinearTransform {
     41   int64_t  a_zero;
     42   int64_t  b_zero;
     43   int32_t  a_to_b_numer;
     44   uint32_t a_to_b_denom;
     45 
     46   // Transform from A->B
     47   // Returns true on success, or false in the case of a singularity or an
     48   // overflow.
     49   bool doForwardTransform(int64_t a_in, int64_t* b_out) const;
     50 
     51   // Transform from B->A
     52   // Returns true on success, or false in the case of a singularity or an
     53   // overflow.
     54   bool doReverseTransform(int64_t b_in, int64_t* a_out) const;
     55 
     56   // Helpers which will reduce the fraction N/D using Euclid's method.
     57   template <class T> static void reduce(T* N, T* D);
     58   static void reduce(int32_t* N, uint32_t* D);
     59 };
     60 
     61 
     62 }
     63 
     64 #endif  // _LIBS_UTILS_LINEAR_TRANSFORM_H
     65