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Multiplication Section
3-7
Central Processing Unit
Table 3–1. Product Shift Modes for the Product-Scaling Shifter
PM Shift Comments
00 no shift Product sent to CALU or data write bus (DWEB) with no shift
01 left 1 Removes the extra sign bit generated in a 2s-complement multiply
to produce a Q31 product
†
10 left 4 Removes the extra four sign bits generated in a 16-bit × 13-bit 2s-
complement multiply to produce a Q31 product
†
when multiplying
by a 13-bit constant
11 right 6 Scales the product to allow up to 128 product accumulations with-
out overflowing the accumulator. The right shift is always sign ex-
tended, regardless of the value of the sign-extension mode bit
(SXM) of status register ST1.
†
A Q31 number is a binary fraction in which there are 31 digits to the right of the binary point
(the base 2 equivalent of the base 10 decimal point).