Motorola CPU32 Bedienungsanleitung PDF herunterladen (Seite 409)

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101

Floating Point Instructions

MOTOROLA M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL 5-107

FSCALE Scale Exponent FSCALE

(MC6888X, M68040FPSP)

Operation: FPn x INT(2Source) → FPn

Assembler FSCALE. < fmt > < ea > ,FPn

Syntax: FSCALE.X FPm,FPn

Attributes: Format = (Byte, Word, Long, Single, Double, Extended, Packed)

Description: Converts the source operand to an integer (if necessary) and adds that integer

to the destination exponent. Stores the result in the destination ﬂoating-point data

Source

, but is

much faster than a multiply operation when the source is an integer value.

The floating-point coprocessor assumes that the scale factor is an integer value before

the operation is executed. If not, the value is chopped (i.e., rounded using the round-

to-zero mode) to an integer before it is added to the exponent. When the absolute value

of the source operand is ≥ 2

, an overflow or underflow always results.

Operation Table:

NOTES:

1. If the source operand is a NAN, refer to 1.6.5 Not-A-Numbers for more information.

2. Returns the value of FPn before the operation. However, the result is

processed by the normal instruction termination procedure to round it as

required. Thus, an overﬂow and/or inexact result may occur if the rounding

precision has been changed to a smaller size since the FPn value was

loaded.

3. Sets the OPERR bit in the ﬂoating-point status register exception byte.

DESTINATION

SOURCE

+ In Range – + Zero – + Infinity –

In Range + – Scale Exponent FPn

NAN

Zero + –

+ 0.0 – 0.0 + 0.0 – 0.0

NAN

Infinity + –

+ inf – inf + inf – inf

NAN

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