ctzw
Count trailing zero bits in word
This instruction is defined by:
Synopsis
This instruction 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 of the least-significant word (i.e., 31). Accordingly, if the least-significant word is 0, the output is 32, and if the least-significant bit of the input is a 1, the output is 0.
Execution
-
Pruned, XLEN == 64
-
Original
X[rd] = (63) - $signed(lowest_set_bit(X[rs1][31:0]));
if (implemented?(ExtensionName::B) && (CSR[misa].B == 1'b0)) {
raise(ExceptionCode::IllegalInstruction, mode(), $encoding);
}
X[rd] = (xlen() - 1) - $signed(lowest_set_bit(X[rs1][31:0]));