diff options
Diffstat (limited to 'mysys/my_bit.c')
| -rw-r--r-- | mysys/my_bit.c | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/mysys/my_bit.c b/mysys/my_bit.c index 0ff487afe03..55dd72f5f76 100644 --- a/mysys/my_bit.c +++ b/mysys/my_bit.c @@ -29,3 +29,45 @@ uint my_bit_log2(ulong value) for (bit=0 ; value > 1 ; value>>=1, bit++) ; return bit; } + +static char nbits[256] = { + 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, + 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, + 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, + 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, + 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, + 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, + 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, + 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, + 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, + 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, + 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, + 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, + 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, + 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, + 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, + 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8, +}; + +uint my_count_bits(ulonglong v) +{ +#if SIZEOF_LONG_LONG > 4 + /* The following code is a bit faster on 16 bit machines than if we would + only shift v */ + ulong v2=(ulong) (v >> 32); + return (uint) (uchar) (nbits[(uchar) v] + + nbits[(uchar) (v >> 8)] + + nbits[(uchar) (v >> 16)] + + nbits[(uchar) (v >> 24)] + + nbits[(uchar) (v2)] + + nbits[(uchar) (v2 >> 8)] + + nbits[(uchar) (v2 >> 16)] + + nbits[(uchar) (v2 >> 24)]); +#else + return (uint) (uchar) (nbits[(uchar) v] + + nbits[(uchar) (v >> 8)] + + nbits[(uchar) (v >> 16)] + + nbits[(uchar) (v >> 24)]); +#endif +} + |