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Motorola DSP96002 User Manual

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MOTOROLA

DSP96002 USER’S MANUAL

D-21

D.1.5.1.2.2

Results Rounded To SP That Are Normalized

If the Data ALU operation result was rounded to SP and the rounded result may be represented as a nor-

malized single precision floating-point number, the result will be stored in normalized DP format that may

be read out by single and double precision moves without errors or truncation.

D.1.5.1.2.3

Results Rounded To SP That Are Denormalized

If the Data ALU operation result was rounded to SP and the rounded result must be represented as a de-

normalized single precision floating-point number, the result will be stored in unnormalized DP format with

the U tag set and the I bit cleared, and it may be read out by single precision moves without errors or trun-

cation. If the register is read by a double precision move, completely incorrect data will be obtained; see

the discussion in Section C.3.2.

In this case, before the result is delivered, an additional Data ALU execution cycle is required in which the

SEP mantissa is shifted right the required number of places for correct rounding to SP.

The presence of unnormalized numbers in DP format will add one dummy cycle followed by an additional

cycle for each unnormalized DP operand to any Data ALU operation that uses them as input. During the

additional cycle the unnormalized operand (U-TAG=1) is normalized, however the register itself will not be

modified.

D.1.5.1.2.4

Results Rounded To SEP

Data ALU results are rounded to SEP when the instruction is specified with the .X suffix (FMPY.X, FADD.X,

etc.).

D.1.5.1.2.5

Results Rounded To SEP That Are Normalized

If the Data ALU operation result was rounded to SEP and the rounded result may be represented as a nor-

malized single extended precision floating-point number, the result will be stored in normalized DP format

that may be read out by double precision moves without errors or truncation.

If the result stored in the register is read with a single precision move, two situations may occur:

1.

The SEP exponent is in the range of the normalized SP exponent: the data read will be round-
ed to SP by truncating the SEP mantissa; this is equivalent to IEEE round towards zero.

2.

The SEP exponent is not in the range of the normalized SP exponent: the data read will not
have the right exponent. The correct value should have been infinity, zero or a denormalized
SP, but the move instruction does not provide it.

D.1.5.1.2.6

Results Rounded To SEP That Are Denormalized

If the Data ALU operation result was rounded to SEP and the rounded result must be represented as a

denormalized single extended precision floating-point number, the result will be stored in normalized DP

format with the V tag set and I bit cleared, and it may be read out by double precision

moves without errors or truncation. If the register is read by a single precision move, completely incorrect

data will be obtained; see the discussion in Section C.3.3 (double precision and single extended precision

numbers have the same exponent bias).