Motorola once sc140 Manual De Usuario
Hardware Support on StarCore
Introduction to the SC140 Tools
5
2
Integer and Fractional Arithmetic Exercise
One of the strengths of both the StarCore architecture and the StarCore compiler is the ability to perform
both fractional and integer arithmetic. This exercise presents a reminder about integer and fractional
arithmetic representation and then shows how to use the StarCore compiler fractional intrinsics. Values
stored in memory or registers are interpreted differently depending on the operation performed. For
integers, the binary point is considered to be immediately to the right of the LSB. For the fractional case,
the binary point is considered to be immediately to the right of the MSB. Table 1 illustrates this for 16-bit
data values.
both fractional and integer arithmetic. This exercise presents a reminder about integer and fractional
arithmetic representation and then shows how to use the StarCore compiler fractional intrinsics. Values
stored in memory or registers are interpreted differently depending on the operation performed. For
integers, the binary point is considered to be immediately to the right of the LSB. For the fractional case,
the binary point is considered to be immediately to the right of the MSB. Table 1 illustrates this for 16-bit
data values.
2.1 Hardware Support on StarCore
StarCore has a dual instruction set for operations that produce different results depending on whether
fractional or integer arithmetic is used. The instruction set is complementary when an integer or a
fractional operation leads to the same result, regardless of the operation type: for example, an addition.
fractional or integer arithmetic is used. The instruction set is complementary when an integer or a
fractional operation leads to the same result, regardless of the operation type: for example, an addition.
The instruction set is dual (as shown in Table 2) in two cases, which automatically take care of data
alignment, zero filling, and sign extension:
alignment, zero filling, and sign extension:
•
when an integer or a fractional operation leads to a different result depending on the operation
type: for example, a multiplication.
type: for example, a multiplication.
•
when data is transferred from/to memory.
Table 1. Interpretation of 16-bit Integer and Fractional Data Values
Binary Representation
Hexadecimal
Representation
Integer Value
(decimal)
Fractional value
(decimal)
0100 0000 0000 0000
0x4000
16384
0.5
0001 0000 0000 0000
0x1000
4096
0.125
0000 0000 0000 0000
0x0000
0
0.0
1100 0000 0000 0000
0xC000
-16384
-0.5
1111 0000 0000 0000
0xF000
-4096
-0.125
Table 2. Fractional and Integer Assembly Language Instructions
Operation
Integer
Fractional
Multiply
impy
mpy
Multiply accumulate
imac
mac
Move
move.b, move.w,
move.2w, move.4w
move.f, move.2f, move.4f