74 lines
2.1 KiB
C++
74 lines
2.1 KiB
C++
/* Copyright 2018 Dirk Steinke
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License. */
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#include "pch.h"
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#include "bit_helper.h"
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unsigned bitLength(unsigned value) {
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unsigned l = 0;
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while (value > 0) {
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l++;
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value >>= 1;
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}
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return l;
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}
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static unsigned char reverse4[16] = {0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15};
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static unsigned bitReverse8(const unsigned value) {
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return (reverse4[value & 0x0f] << 4) | reverse4[(value >> 4) & 0x0f];
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}
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static unsigned bitReverse16(const unsigned value) {
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return (bitReverse8(value & 0xff) << 8) | bitReverse8(value >> 8);
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}
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static unsigned bitReverse32(const unsigned value) {
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return (bitReverse16(value & 0xffff) << 16) | bitReverse16(value >> 16);
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}
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unsigned bitReverse(const unsigned value, const unsigned bits) {
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if (bits <= 8) {
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return bitReverse8(value) >> (8 - bits);
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}
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if (bits <= 16) {
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return bitReverse16(value) >> (16 - bits);
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}
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return bitReverse32(value) >> (32 - bits);
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}
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static unsigned char leading4[16] = {4, 3, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0};
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unsigned bitLeadingZeroes(const unsigned value_) {
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if (value_ == 0) {
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return 32;
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}
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unsigned value = value_;
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unsigned result = 0;
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while ((value & 0xf0000000) == 0) {
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value <<= 4;
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result += 4;
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}
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return result + leading4[value >> 28];
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}
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static unsigned char trailing4[16] = {4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0};
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unsigned bitTrailingZeroes(const unsigned value_) {
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if (value_ == 0) {
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return 32;
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}
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unsigned value = value_;
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unsigned result = 0;
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while ((value & 0xf) == 0) {
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value >>= 4;
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result += 4;
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}
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return result + trailing4[value & 0xf];
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}
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