There were math co-processor boards (AM9511, AM9512, for example) for
S100 systems. ISTR that there was even a TRW bipolar (16x16? Huge
chip that ran hot as a pistol) for the S100 bus.
There was am 8*8 (I think) parallel multiplier chip in the 74xxx TTL
family. 40 pin thing. I've come across it twice. Once in an early
electronic still camera (to multiply the outptus of the ADC by the values
storted in a compensation EPROM, and thus handle the non-uniform repsonse
of the CCD). The other time was in a leased-line modem which seems to
implement some kind of DSP using this chip and, IIRC, 2900 series.
-tony