log2.h

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#ifndef __LOG2_H__
#define __LOG2_H__
 
#include <common/bitops.h>
 
/* clang-format off */
#define ilog2(x)                  \
(                                 \
    __builtin_constant_p(x) ? (   \
        (x) < 1 ? __ilog2_NaN() : \
        (x) & (1ul << 31) ? 31 :  \
        (x) & (1ul << 30) ? 30 :  \
        (x) & (1ul << 29) ? 29 :  \
        (x) & (1ul << 28) ? 28 :  \
        (x) & (1ul << 27) ? 27 :  \
        (x) & (1ul << 26) ? 26 :  \
        (x) & (1ul << 25) ? 25 :  \
        (x) & (1ul << 24) ? 24 :  \
        (x) & (1ul << 23) ? 23 :  \
        (x) & (1ul << 22) ? 22 :  \
        (x) & (1ul << 21) ? 21 :  \
        (x) & (1ul << 20) ? 20 :  \
        (x) & (1ul << 19) ? 19 :  \
        (x) & (1ul << 18) ? 18 :  \
        (x) & (1ul << 17) ? 17 :  \
        (x) & (1ul << 16) ? 16 :  \
        (x) & (1ul << 15) ? 15 :  \
        (x) & (1ul << 14) ? 14 :  \
        (x) & (1ul << 13) ? 13 :  \
        (x) & (1ul << 12) ? 12 :  \
        (x) & (1ul << 11) ? 11 :  \
        (x) & (1ul << 10) ? 10 :  \
        (x) & (1ul <<  9) ?  9 :  \
        (x) & (1ul <<  8) ?  8 :  \
        (x) & (1ul <<  7) ?  7 :  \
        (x) & (1ul <<  6) ?  6 :  \
        (x) & (1ul <<  5) ?  5 :  \
        (x) & (1ul <<  4) ?  4 :  \
        (x) & (1ul <<  3) ?  3 :  \
        (x) & (1ul <<  2) ?  2 :  \
        (x) & (1ul <<  1) ?  1 :  \
        (x) & (1ul <<  0) ?  0 :  \
        __ilog2_NaN()             \
        ) :                       \
        __ilog2(x)                \
)
/* clang-format on */
 
static inline unsigned long __ilog2(unsigned long x)
{
    return _flsl(x) - 1;
}
 
static inline /*__atrribute__(noreturn)*/ unsigned long __ilog2_NaN(void)
{
    while (1)
        ;
    return 0;
}
 
#endif