1 files changed, 64 insertions, 0 deletions
diff --git a/src/dsp/inverse_transform.inc b/src/dsp/inverse_transform.inc
new file mode 100644
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+++ b/src/dsp/inverse_transform.inc
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+// Copyright 2019 The libgav1 Authors
+//
+// 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.
+
+// Constants and utility functions used for inverse transform implementations.
+// This will be included inside an anonymous namespace on files where these are
+// necessary.
+
+// The value at index i is derived as: round(cos(pi * i / 128) * (1 << 12)).
+constexpr int16_t kCos128[65] = {
+    4096, 4095, 4091, 4085, 4076, 4065, 4052, 4036, 4017, 3996, 3973,
+    3948, 3920, 3889, 3857, 3822, 3784, 3745, 3703, 3659, 3612, 3564,
+    3513, 3461, 3406, 3349, 3290, 3229, 3166, 3102, 3035, 2967, 2896,
+    2824, 2751, 2675, 2598, 2520, 2440, 2359, 2276, 2191, 2106, 2019,
+    1931, 1842, 1751, 1660, 1567, 1474, 1380, 1285, 1189, 1092, 995,
+    897,  799,  700,  601,  501,  401,  301,  201,  101,  0};
+
+inline int16_t Cos128(int angle) {
+  angle &= 0xff;
+
+  // If |angle| is 128, this function returns -4096 (= -2^12), which will
+  // cause the 32-bit multiplications in ButterflyRotation() to overflow if
+  // dst[a] or dst[b] is -2^19 (a possible corner case when |range| is 20):
+  //
+  //   (-2^12) * (-2^19) = 2^31, which cannot be represented as an int32_t.
+  //
+  // Note: |range| is 20 when bitdepth is 12 and a row transform is performed.
+  //
+  // Assert that this angle is never used by DCT or ADST.
+  assert(angle != 128);
+  if (angle <= 64) return kCos128[angle];
+  if (angle <= 128) return -kCos128[128 - angle];
+  if (angle <= 192) return -kCos128[angle - 128];
+  return kCos128[256 - angle];
+}
+
+inline int16_t Sin128(int angle) { return Cos128(angle - 64); }
+
+// The value for index i is derived as:
+// round(sqrt(2) * sin(i * pi / 9) * 2 / 3 * (1 << 12)).
+constexpr int16_t kAdst4Multiplier[4] = {1321, 2482, 3344, 3803};
+
+constexpr uint8_t kTransformRowShift[kNumTransformSizes] = {
+    0, 0, 1, 0, 1, 1, 2, 1, 1, 2, 1, 2, 2, 1, 2, 1, 2, 1, 2};
+
+constexpr bool kShouldRound[kNumTransformSizes] = {
+    false, true,  false, true, false, true, false, false, true, false,
+    true,  false, false, true, false, true, false, true,  false};
+
+constexpr int16_t kIdentity4Multiplier /* round(2^12 * sqrt(2)) */ = 0x16A1;
+constexpr int16_t kIdentity4MultiplierFraction /* round(2^12 * (sqrt(2) - 1))*/
+    = 0x6A1;
+constexpr int16_t kIdentity16Multiplier /* 2 * round(2^12 * sqrt(2)) */ = 11586;
+constexpr int16_t kTransformRowMultiplier /* round(2^12 / sqrt(2)) */ = 2896;