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71 lines
1.6 KiB
C
71 lines
1.6 KiB
C
/*
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* BIRD Library -- Generic Bit Operations
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*
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* (c) 1998 Martin Mares <mj@ucw.cz>
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*
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* Can be freely distributed and used under the terms of the GNU GPL.
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*/
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#ifndef _BIRD_BITOPTS_H_
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#define _BIRD_BITOPTS_H_
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#include "sysdep/config.h"
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/*
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* Bit mask operations:
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*
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* u32_mkmask Make bit mask consisting of <n> consecutive ones
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* from the left and the rest filled with zeroes.
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* E.g., u32_mkmask(5) = 0xf8000000.
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* u32_masklen Inverse operation to u32_mkmask, -1 if not a bitmask.
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*
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* u32_log2
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* u64_log2 Find the first 1 in the number
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*
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* u32_hash Compute a common hash
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*
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* u64_var_encode Encode a variable-length bitstring into fixed-length u64
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* u64_var_decode Decode the bitstring
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*/
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u32 u32_mkmask(uint n);
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uint u32_masklen(u32 x);
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u32 u32_log2(u32 v);
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u64 u64_log2(u64 v);
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static inline u32 u32_hash(u32 v) { return v * 2902958171u; }
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static inline u8 u32_popcount(u32 v) { return __builtin_popcount(v); }
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static inline u64 u64_var_encode(u64 data, uint padlen)
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{
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ASSERT(padlen > 0);
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/* Append the other bit than the last */
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if (data & 1)
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return data << padlen;
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else
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return (data << padlen) | ((1ULL << padlen) - 1);
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}
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static inline u64 u64_var_decode(u64 enc, uint *padlen)
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{
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/* If enc is ....|100..00, then cpl is ....|011..11
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* If enc is ....|011..11, then cpl is ....|100..00
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*
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* In both cases, enc ^ cpl is then 0...0|111..11
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* so u64_log2((enc ^ cpl) + 1) is the number of bits to shift right.
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* */
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u64 cpl = (enc & 1) ? (enc + 1) : (enc - 1);
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if ((~enc == 0) || (~cpl == 0)) {
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*padlen = 64;
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return 0;
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} else {
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*padlen = u64_log2(enc ^ cpl);
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return enc >> *padlen;
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}
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}
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#endif
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