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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.
1.15 NUMBER
(HEXADECIMAL)
0x0001
0x7FFF
0xFFFF
0x8000
0
-2
2
Figure 2-2. Bit Weighting for 1.15 Numbers
ADSP-BF53x/BF56x Blackfin Processor Programming Reference
DECIMAL
EQUIVALENT
0.000031
0.999969
–0.000031
–1.000000
–1
–2
–3
–4
–5
–6
2
2
2
2
2
Computational Units
–7
–8
–9
–10
–11
–12
2
2
2
2
2
2
–13
–14
–15
2
2
2
2-5
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