ffs

Find First Set. Used in Linux programming as a quick way to find which is the first bit of a word, starting from the least significant bit, that is set.

From the Linux kernel arch/x86/kernel/cpu/mtrr/generic.c:

high_width = ffs(size_or_mask & 0xffffffffUL) - 1;

high_width becomes the bit position of the least significant bit set in size_or_mask. Note, the least significant bit for ffs is 1, not 0, because 0 is returned if no bit is set. The -1 is used to convert the result of ffs() to the standard bit numbering.

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