General Description: When I use the 18x18 signed multiplier for the Virtex-II multiplier core in D_IP2 (Mult_gen_v2_0), the multiplier uses 4 multiplier blocks instead of 1.
This occurs because of the way in which the multiplier was coded. When coding work began on mult_gen_v2_0, the Virtex-II "fabric" was still somewhat unclear; subsequently, when the coding for the 18x18 block-multiplier was done, a subtle mistake was made. Although the block multiplier can cope with 18-bit signed numbers, the IP developers didn't realize this at the time, and thought that the addition of the sign bit would necessitate the use of several block-multipliers to perform this task.
This issue has been fixed in D_IP3, which was released on March 9, 2001.