The FirstNonzeroBit command locates the first nonzero bit in a number in a specified direction from a specified location.

If dir is specified as lower, then the number will be searched in the direction of the most significant bit to the least significant bit.

If dir is specified as higher, then the number will be searched in the direction of the least significant bit to the most significant bit.

$\mathrm{with}\left(\mathrm{Bits}\right)\:$

$\mathrm{FirstNonzeroBit}\left(255\right)=\mathrm{ilog2}\left(255\right)$

$7=7$

$\mathrm{FirstNonzeroBit}\left(256\right)=\mathrm{ilog2}\left(256\right)$

$8=8$

$\mathrm{FirstNonzeroBit}\left(0\right)\ne \mathrm{ilog2}\left(0\right)$

$\mathrm{-1}\ne -\mathrm{\infty }$

$\mathrm{FirstNonzeroBit}\left(1+2+4+256\,\mathrm{higher}\right)$

$0$

$\mathrm{FirstNonzeroBit}\left(1+2+4+256\,\mathrm{higher}\,1\right)$

$1$

$\mathrm{FirstNonzeroBit}\left(1+2+4+256\,\mathrm{higher}\,2\right)$

$2$

$\mathrm{FirstNonzeroBit}\left(1+2+4+256\,\mathrm{higher}\,3\right)$

$8$

$\mathrm{FirstNonzeroBit}\left(1+2+4+256\,\mathrm{higher}\,9\right)$

$\mathrm{\infty }$

$\mathrm{FirstNonzeroBit}\left(-1\,\mathrm{lower}\right)$

$\mathrm{\infty }$

$\mathrm{FirstNonzeroBit}\left(-1\,\mathrm{lower}\,5\right)$

$5$