Motorola CPU32 User Manual download pdf (Page 30)

100

101

Introduction

MOTOROLA M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL 1-19

1.6.3 Zeros

Zeros can be positive or negative and represent the real values + 0.0 and – 0.0 (see Figure

1-15).

1.6.4 Infinities

Inﬁnities can be positive or negative and represent real values that exceed the overﬂow

threshold. A result’s exponent greater than or equal to the maximum exponent value

indicates the overﬂow for a given data format and operation. This overﬂow description

ignores the effects of rounding and the user-selectable rounding models. For single- and

double-precision inﬁnities the fraction is a zero. For extended-precision inﬁnities, the

mantissa’s MSB, the explicit integer bit, can be either one or zero (see Figure 1-16).

1.6.5 Not-A-Numbers

When created by the FPU, NANs represent the results of operations having no

mathematical interpretation, such as inﬁnity divided by inﬁnity. All operations involving a

NAN operand as an input return a NAN result. When created by the user, NANs can protect

against unitialized variables and arrays or represent user-deﬁned data types. For extended-

precision NANs, the mantissa’s MSB, the explicit integer bit, can be either one or zero (see

Figure 1-17).

The FPU implements two different types of NANs identiﬁed by the value of the MSB of the

mantissa for single- and double-precision, and the MSB of the mantissa minus one for

extended-precision. If the bit is set, it is a nonsignaling NAN, otherwise, it is an SNAN. An

Figure 1-15. Zero Format

Figure 1-16. Infinity Format

Figure 1-17. Not-A-Number Format

EXPONENT = 0 MANTISSA = 0

SIGN OF MANTISSA, 0 OR 1

EXPONENT = MAXIMUM

MANTISSA = 0

SIGN OF MANTISSA, 0 OR 1

EXPONENT = MAXIMUM

MANTISSA = ANY NONZERO BIT PATTERN

SIGN OF MANTISSA, 0 OR 1

1 2 ... 25 26 27 28 29 30 31 32 33 34 35 ... 645 646

Comments to this Manuals

No comments

Motorola CPU32 User Manual Page 30

Comments to this Manuals

Related products and manuals for Processors Motorola CPU32