DALU

The following table (Table 2-11) shows the arithmetic saturation and rounding operations for the four possible cases of scaling, no scaling, and arithmetic saturation mode on/off.

 

 

Table 2-11. Saturation and Rounding Interactions

 

 

 

 

 

 

 

Scaling

Arithmetic

Arithmetic Saturation

 

 

 

 

 

 

Saturation

 

 

 

Rounding

Selected

Saturable DALU

 

 

Mode

Special Six Instructions

 

 

 

Instructions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

None

Off

None

None

 

Rounding with no scaling

 

 

 

 

 

 

Up/down

Off

None

None

 

Rounding with scaling

 

 

 

 

 

considered

 

 

 

 

 

 

None

On

Saturation can occur

None

 

Rounding with no scaling

 

 

 

 

 

 

Up/down

On

Saturation can occur, no

None

 

Rounding with no scaling

 

 

scaling considered

 

 

 

 

 

 

 

 

 

2.2.2 DALU Arithmetic and Rounding

The following paragraphs describe the DALU data representation, rounding modes, and arithmetic methods.

2.2.2.1 Data Representation

The SC140 core uses either a fractional or integer two’s complement data representation for all DALU operations. The main difference between fractional and integer representations is the location of the decimal (or binary) point. For fractional arithmetic, the decimal (or binary) point is always located immediately to the right of the most significant bit of the high portion. For integer values, it is always located immediately to the right of the least significant bit (LSB) of the value. Figure 2-3 shows the location of the decimal point (binary point) bit weighting and operand alignment for different fractional and integer representations supported on the SC140 architecture.

SC140 DSP Core Reference Manual

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Image 49
Freescale Semiconductor SC140 Dalu Arithmetic and Rounding, Data Representation, Saturation and Rounding Interactions