ctz
Count trailing zero bits
Counts the number of 0’s before the first 1, starting at the least-significant bit (i.e., 0) and progressing to the most-significant bit (i.e., XLEN-1). Accordingly, if the input is 0, the output is XLEN, and if the least-significant bit of the input is a 1, the output is 0.
Execution
if (implemented?(ExtensionName::B) && (CSR[misa].B == 1'b0)) {
raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
if (xlen() == 32) {
X[xd] = lowest_set_bit(X[xs1][31:0]);
} else {
X[xd] = lowest_set_bit(X[xs1]);
}