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cd23580cc5
Sometimes there's a bunch of junk in the binary that isn't used for anything. Often it's there to make things line up at the start of a page boundary. This adds a ".junk" directive that tells the disassembler that it can safely disregard the contents of a region. If the region ends on a power-of-two boundary, an alignment value can be specified. The assembly source generators will output an alignment directive when possible, a .fill directive when appropriate, and a .dense directive when all else fails. Because we're required to regenerate the original data file, it's not always possible to avoid generating a hex dump.
95 lines
3.7 KiB
C#
95 lines
3.7 KiB
C#
/*
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* Copyright 2019 faddenSoft
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*
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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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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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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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*/
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using System;
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namespace CommonUtil {
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public class BitTwiddle {
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/// <summary>
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/// Returns the argument, rounded up to the next highest power of 2. If the argument
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/// is an exact power of two, it is returned unmodified.
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/// </summary>
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public static int RoundUpPowerOf2(int val) {
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val--; // handle exact power of 2 case; works correctly for val=0
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return NextHighestPowerOf2(val);
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}
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/// <summary>
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/// Returns the first power of 2 value that is higher than val. If the argument is
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/// an exact power of two, the next power of 2 is returned.
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/// </summary>
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/// <remarks>
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/// Classic bit-twiddling approach. I can't find a "count leading zeroes" function
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/// in C# that turns into a CPU instruction; if we had that, we could just use 1<<N.
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/// </remarks>
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public static int NextHighestPowerOf2(int val) {
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val |= val >> 1; // "smear" bits across integer
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val |= val >> 2;
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val |= val >> 4;
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val |= val >> 8;
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val |= val >> 16;
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return val + 1;
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}
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/// <summary>
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/// Returns an integer in which the only bit set is the least-significant set bit in
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/// the argument.
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/// </summary>
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/// <remarks>
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/// If you pass in 10110100, this will return 00000100.
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///
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/// Two's complement negation inverts and adds one, so 01100 --> 10011+1 --> 10100. The
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/// only set bit they have in common is the one we want.
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/// </remarks>
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public static int IsolateLeastSignificantOne(int val) {
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return val & -val;
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}
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/// <summary>
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/// Returns the number of bits that are set in the argument.
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/// </summary>
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/// <remarks>
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/// If you pass in 10110100, this will return 4.
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///
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/// This comes from http://aggregate.org/MAGIC/#Population%20Count%20(Ones%20Count) .
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/// </remarks>
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public static int CountOneBits(int val) {
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// 32-bit recursive reduction using SWAR...
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// but first step is mapping 2-bit values
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// into sum of 2 1-bit values in sneaky way
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val -= ((val >> 1) & 0x55555555);
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val = (((val >> 2) & 0x33333333) + (val & 0x33333333));
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val = (((val >> 4) + val) & 0x0f0f0f0f);
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val += (val >> 8);
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val += (val >> 16);
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return (val & 0x0000003f);
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}
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/// <summary>
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/// Returns the number of trailing zero bits in the argument.
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/// </summary>
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/// <remarks>
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/// If you pass in 10110100, this will return 2.
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///
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/// Also from http://aggregate.org/MAGIC/ .
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/// </remarks>
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public static int CountTrailingZeroes(int val) {
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// Lazy: reduce to least-significant 1 bit, subtract one to clear that bit and set
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// all the bits to the right of it, then just count the 1s.
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return CountOneBits(IsolateLeastSignificantOne(val) - 1);
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}
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}
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}
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