Initial version of astc-codec for open source release

Contains an implementation of an ASTC decoder that is able to pass the
dEQP ASTC LDR tests.

astc-codec has no external dependencies for the main library, only for
test code, and is licensed under the Apache license.

Components:

include/ - Public API that can decode ASTC LDR data into a RGBA UNORM8
buffer.

src/base/ - Base library with common functionality not directly related
to ASTC decoding.  Contains a uint128 implementation, BitStream for
reading/writing bits with a primitive (or uint128 type), Optional
implementation (to not take a dependency on C++17), and more.

src/decoder/ - Internal implementation of the ASTC decoder.

src/base/test/, src/decoder/test/ - Unit tests (and a fuzzing test) for
the astc decoder.

src/decoder/testdata/ - Sample ASTC images and golden image results for
testing.

src/decoder/tools/ - A tool to inspect contents of an ASTC file.

third_party/ - Third party libraries, only used for tests.

Change-Id: Ia98e5a7dc847daa3d3a48c5e62d94b8fb1cb98bd

1 files changed, 80 insertions, 0 deletions

diff --git a/src/base/math_utils.h b/src/base/math_utils.h
new file mode 100644
index 0000000..48f1a24
--- /dev/null
+++ b/src/base/math_utils.h
@@ -0,0 +1,80 @@
+// Copyright 2018 Google LLC
+//
+// 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
+//
+//     https://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 ASTC_CODEC_BASE_MATH_UTILS_H_
+#define ASTC_CODEC_BASE_MATH_UTILS_H_
+
+#include "src/base/uint128.h"
+
+#include <cassert>
+#include <cstdint>
+#include <type_traits>
+
+namespace astc_codec {
+namespace base {
+
+inline int Log2Floor(uint32_t n) {
+  if (n == 0) {
+    return -1;
+  }
+
+  int log = 0;
+  uint32_t value = n;
+  for (int i = 4; i >= 0; --i) {
+    int shift = (1 << i);
+    uint32_t x = value >> shift;
+    if (x != 0) {
+      value = x;
+      log += shift;
+    }
+  }
+  assert(value == 1);
+  return log;
+}
+
+inline int CountOnes(uint32_t n) {
+  n -= ((n >> 1) & 0x55555555);
+  n = ((n >> 2) & 0x33333333) + (n & 0x33333333);
+  return static_cast<int>((((n + (n >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24);
+}
+
+template<typename T>
+inline T ReverseBits(T value) {
+  uint32_t s = sizeof(value) * 8;
+  T mask = ~T(0);
+  while ((s >>= 1) > 0) {
+    mask ^= (mask << s);
+    value = ((value >> s) & mask) | ((value << s) & ~mask);
+  }
+
+  return value;
+}
+
+template<typename T>
+inline T GetBits(T source, uint32_t offset, uint32_t count) {
+  static_assert(std::is_same<T, UInt128>::value || std::is_unsigned<T>::value,
+                "T must be unsigned.");
+
+  const uint32_t total_bits = sizeof(T) * 8;
+  assert(count > 0);
+  assert(offset + count <= total_bits);
+
+  const T mask = count == total_bits ? ~T(0) : ~T(0) >> (total_bits - count);
+  return (source >> offset) & mask;
+}
+
+}  // namespace base
+}  // namespace astc_codec
+
+#endif  // ASTC_CODEC_BASE_MATH_UTILS_H_