Analog Devices ADSP-BF53x Blackfin, Reference

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ADSP-BF53x/BF56x Blackfin Processor Programming Reference 2-5
Computational Units
Signed Numbers: Two’s-Complement
In ADSP-BF53x/56x processor arithmetic, the word signed refers to
two’s-complement numbers. Most ADSP-BF53x/56x processor family
operations presume or support two’s-complement arithmetic.
Fractional Representation: 1.15
ADSP-BF53x processor arithmetic is optimized for numerical values in a
fractional binary format denoted by 1.15 (“one dot fifteen”). In the 1.15
format, 1 sign bit (the Most Significant Bit (MSB)) and 15 fractional bits
represent values from –1 to 0.999969.
Figure 2-2 shows the bit weighting for 1.15 numbers as well as some
examples of 1.15 numbers and their decimal equivalents.
Figure 2-2. Bit Weighting for 1.15 Numbers
-2
0
2
–1
2
–2
2
–3
2
–4
2
–5
2
–6
2
–7
2
–8
2
–9
2
–10
2
–11
2
–12
2
–13
2
–14
2
–15
1.15 NUMBER
(HEXADECIMAL)
0x0001 0.000031
0x7FFF 0.999969
0xFFFF –0.000031
0x8000 –1.000000
DECIMAL
EQUIVALENT