In an ideal DDS, the width of the input bus to the map is the same as the width of the accumulator output bus (that is, N equals P). This is impractical, however, if N is large. For example, an ideal DDS with a 32-bit accumulator would require a map with 2 to the 32 entries. Such a map would contain over 4-billion D-bit values. A ideal 48-bit DDS would need a map with over 280-trillion D-bit values! This is clearly not practical. To get around this problem, a typical DDS relies on truncating the N-bit accumulator output at the input to the map. This is accomplished by retaining the P most significant bits of the N-bit accumulator output as the input to the map. This is known as phase truncation and can significantly reduce the size of the map in cases where N is large. Consequently, in a DDS employing phase truncation, P is always less than N.