Add a linear transform library to libutils

Change-Id: Icdec5a6bebd9d8f24b3f335f8ec8b09a5810a774

1 files changed, 64 insertions, 0 deletions

diff --git a/include/utils/LinearTransform.h b/include/utils/LinearTransform.h
new file mode 100644
index 0000000..04cb355
--- /dev/null
+++ b/include/utils/LinearTransform.h
@@ -0,0 +1,64 @@
+/*
+ * 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