From b56a50064caf2a590ba43699e0074690fcd431bf Mon Sep 17 00:00:00 2001
From: Jeff McGlynn <jwmcglynn@google.com>
Date: Wed, 20 Jun 2018 11:34:20 -0700
Subject: 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
---
 src/decoder/quantization.h | 65 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 src/decoder/quantization.h

(limited to 'src/decoder/quantization.h')

diff --git a/src/decoder/quantization.h b/src/decoder/quantization.h
new file mode 100644
index 0000000..5f7239f
--- /dev/null
+++ b/src/decoder/quantization.h
@@ -0,0 +1,65 @@
+// 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_DECODER_QUANTIZATION_H_
+#define ASTC_CODEC_DECODER_QUANTIZATION_H_
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// ASTC Quantization procedures.
+//
+// The values stored in ASTC blocks tend to be stored in a range much more
+// restricted than the logical range used. For example, sometimes weights are
+// stored in the range from [0, 3] but are used in the range [0, 64]. The
+// process of translating a value to or from this range is known as quantization
+// and dequantization. The ranges to which these values can be (de)quantized
+// are defined by ISERange[Begin|End]() in integer_sequence_codec.h
+
+namespace astc_codec {
+
+// The minimum possible range for a pair of endpoints. If endpoints are
+// quantized to something smaller than this, then it would constitute an
+// illegal ASTC encoding.
+constexpr int kEndpointRangeMinValue = 5;
+
+// The maximum possible range for a weight value. If weights are quantized to
+// something larger than this, then it would constitute an illegal ASTC
+// encoding.
+constexpr int kWeightRangeMaxValue = 31;
+
+// Quantizes a value in the range [0, 255] to [0, |range|]. The quantized values
+// have no correlation to the input values, and there should be no implicit
+// assumptions made about their ordering. Valid values of |range_max_value| are
+// in the interval [5, 255]
+int QuantizeCEValueToRange(int value, int range_max_value);
+
+// Unquantizes a value in the range [0, |range|] to [0, 255]. Performs the
+// inverse procedure of QuantizeValueToRange. Valid values of |range_max_value|
+// are in the interval [5, 255]
+int UnquantizeCEValueFromRange(int value, int range_max_value);
+
+// Quantizes a weight in the range [0, 64] to [0, |range_max_value|]. The
+// quantized values have no correlation to the input values, and there should
+// be no implicit assumptions made about their ordering. Valid values of
+// |range_max_value| are in the interval [1, 31]
+int QuantizeWeightToRange(int weight, int range_max_value);
+
+// Unquantizes a weight in the range [0, |range_max_value|] to [0, 64]. Performs
+// the inverse procedure of QuantizeWeightToRange. Valid values of
+// |range_max_value| are in the interval [1, 31]
+int UnquantizeWeightFromRange(int weight, int range_max_value);
+
+}  // namespace astc_codec
+
+#endif  // ASTC_CODEC_DECODER_QUANTIZATION_H_
-- 
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