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June 2, 2021 08:55
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RefCountedFlags
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| using System; | |
| /// <summary> | |
| /// Provides a boolean value for each value in an enum, | |
| /// but setting the same flag twice means the flags needs to be unset twice to be false | |
| /// </summary> | |
| /// <typeparam name="T">An enum type (optionally with [Flags]) backed by a 32bit int</typeparam> | |
| public unsafe struct RefCountedFlags<T> where T : Enum //T must be backed by a 32bit int | |
| { | |
| fixed byte counts[32]; | |
| public void PushFlags(T val) | |
| { | |
| uint v = (uint)(object)val; | |
| while (v > 0) | |
| { | |
| var idx = FlagToIndex(v); | |
| counts[idx]++; | |
| v &= ~((uint)1 << idx); | |
| } | |
| } | |
| public void PopFlags(T val) | |
| { | |
| uint v = (uint)(object)val; | |
| while (v > 0) | |
| { | |
| var idx = FlagToIndex(v); | |
| counts[idx]--; | |
| v &= ~((uint)1 << idx); | |
| } | |
| } | |
| public bool HasFlag(T val) | |
| { | |
| return counts[FlagToIndex((uint)(object)val)] > 0; | |
| } | |
| private int FlagToIndex(uint v) | |
| { | |
| // Fancy method to find least significant 1 bit | |
| // https://stackoverflow.com/a/757266/915418 | |
| // https://web.archive.org/web/20201106232756/http://supertech.csail.mit.edu/papers/debruijn.pdf | |
| int[] MultiplyDeBruijnBitPosition = | |
| { | |
| 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, | |
| 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9 | |
| }; | |
| return MultiplyDeBruijnBitPosition[((uint)((v & -v) * 0x077CB531U)) >> 27]; | |
| } | |
| } |
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