![]() Then we repeat this scheme all the way up to the rightmost nibble. If the left most nibble is all zeros, then we check the 2nd nibble and if that 2nd nibble contains ones, we return the count in that 2nd nibble ( z) and prepend 4'b0001, that is, 4, because the first nibble was all zeros. With this information for every nibble available we proceed with what is in essence a kind of priority encoder: we first check the leftmost nibble and if it is not all zeros the count will be z, i.e. This count can be 0, 1, 2 or 3 (for all zeros the ai wire will be set.) Each ai wire signals whether the whole nibble consists of zeros, while each duo of z wires counts the leading zeros in the nibble. The for loop instantiates 8 identical pieces of wiring, each piece addressing a 4 bit nibble in the input. The code implements a count leading zeros module with a 32 bit input. So the code below shows a modular implementation.Īssign z = ~((~a & a) | a) Īssign y = ai ? ( // leftmost nibble all zeros?Īi ? ( 6'b100000 // all 32 bits are zero This plays a role in division (where you might need to shift the first bit in the the divisor to align with the dividend) or in floating point operations where for example multiplication requires mantissas that align in order to get the maximum accuracy. It is important to understand the difference between these three as they are very similar and are often confused.īelow is the console output from running the code below in Modelsim: # AND of 1 and 0 is 0īitwise_operators.In many scenarios we need a function to calculate the number of leading zeros in a binary number. If you are looking to test for equality in an if statement, you should check out how to use logical operators. If you only want to operate on the bits of a single input vector, then you are likely looking for the reduction operator. ![]() If one input is not as long as the other, it will automatically be left-extended with zeros to match the length of the other input. The bitwise operators above can operate on either scalars (single bit inputs) or vectors (multiple bit inputs). Refer to this page for a refresher on what each of these truth tables looks like. The table of bit wise operators is shown below: Operator ![]() They take each bit individually and perform a boolean algebra operation with the other input. ![]() The Verilog bitwise operators are used to perform a bit-by-bit operation on two inputs. ![]()
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