Analog Devices ADSP-BF535 Blackfin, Hardware Reference Manual

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Data Types
2-16 ADSP-BF535 Blackfin Processor Hardware Reference
Using Multiplier Integer and Fractional Formats
For multiply-and-accumulate functions, the ADSP-BF535 processor pro-
vides two choices: fractional arithmetic for fractional numbers (1.15) and
integer arithmetic for integers (16.0).
For fractional arithmetic, the 32-bit product output is format adjusted—
sign extended and shifted one bit to the left—before being added to accu-
mulator
A0
or
A1
. For example, bit 31 of the product lines up with bit 32
of
A0
(which is bit 0 of
A0.X
), and bit 0 of the product lines up with bit 1
of
A0
(which is bit 1 of
A0.W
). The LSB is zero filled. The fractional multi-
plier result format appears in Figure 2-4 .
For integer arithmetic, the 32-bit product register is not shifted before
being added to
A0
or
A1
. Figure 2-5 shows the integer mode result
placement.
With either fractional or integer operations, the multiplier output product
is fed into a 40-bit adder/subtracter which adds or subtracts the new prod-
uct with the current contents of the
A0
or
A1
register to produce the final
40-bit result.
Table 2-6. Shifter Arithmetic Formats
Operation Operand Formats Result Formats
Logical Shift Unsigned binary string Same as operands
Arithmetic Shift Signed Same as operands
Exponent Detect Signed Same as operands