DALU

2.2.2.2.2 Signed Integer

This format is used when processing data as integers. Using this format, the N-bit operand is represented using the N.0 bit format (N integer bits). Signed integer numbers lie in the following range:

-2[N-1] SI [2[N-1]-1]

For words and long-word signed integers, the most negative word that can be represented is -32768

($8000) and the most negative long word is -2147483648 ($8000 0000). The most positive word is 32767 ($7FFF) and the most positive long word is 2147483647 ($7FFF FFFF).

If the extension bits are in use, N becomes 40, and the most positive number is 239 – 1 represented by $7F FFFF FFFF. The most negative number is –239, represented by $80 0000 0000.

2.2.2.2.3Unsigned Integer

Unsigned integer numbers may be thought of as positive only. The unsigned numbers have nearly twice the magnitude of a signed number of the same length. Unsigned integer numbers lie in the following range:

0 UI [2N-1]

The binary word is interpreted as having a binary point immediately to the right of the LSB. The most positive 16-bit unsigned integer is 65535 ($FFFF). The most positive 32-bit unsigned integer is 232-1 ($FFFF FFFF). The smallest unsigned number is zero ($0000).

If the extension bits are in use, the range is from zero to +240 – 1.

Table 2-12. Two’s Complement Word Representations

Signed Fractional

Signed Integer

Unsigned Integer

 

 

 

 

 

 

 

 

 

 

 

 

$7FFF

1.0 – 2–15

$7FFF

215 – 1

$FFFF

216 – 1

l

l

l

l

$FFFE

216 – 2

l

l

l

l

l

l

 

 

 

 

 

 

$0001

2–15

$0001

+1

l

l

$0000

0

$0000

0

l

l

 

 

 

 

 

 

$FFFF

–2–15

$FFFF

–1

l

l

l

l

l

l

l

l

 

 

 

 

 

 

l

l

l

l

$0001

1

 

 

 

 

 

 

$8000

–1.0

$8000

–215

$0000

0

SC140 DSP Core Reference Manual

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Image 51
Freescale Semiconductor SC140 specifications Signed Integer, Two’s Complement Word Representations