clz
Count leading zero bits
Counts the number of 0’s before the first 1, starting at the most-significant bit (i.e., XLEN-1) and progressing to bit 0. Accordingly, if the input is 0, the output is XLEN, and if the most-significant bit of the input is a 1, the output is 0.
Execution
X[xd] = (xlen() - 1) - $signed(highest_set_bit(X[xs1]));