Texas-instruments TMS320C3x Uživatelský manuál stáhnout pdf (Strana 146)

100

101

Floating-Point to Integer Conversion (FIX Instruction)

5-41

Data Formats and Floating-Point Operation

5.9 Floating-Point to Integer Conversion (FIX Instruction)

Using the FIX instruction, you can convert an extended-precision floating-

point number to a single-precision integer in a single cycle. The floating-point

to integer conversion of the value

is referred to here as fix(

). The conversion

does not overflow if

, the number to be converted, is in the range:

–2

≤ α ≤ 2

– 1

First, you must be certain that

α(

exp

) ≤ 30

If these bounds are not met, an overflow occurs. If an overflow occurs in the

positive direction, the output is the most positive integer. If an overflow occurs

in the negative direction, the output is the most negative integer. If α(

exp

) is

within the valid range, then α(

man

), with implied bit included, is sign-extended

and right-shifted (rs) by the amount

rs = 31 – α(

exp

)

This right shift (rs) shifts out those bits corresponding to the fractional part of

the mantissa. For example:

If 0 ≤ × < 1, then fix(

) = 0

If –1 ≤ × < 0, then fix(

) = –1

Figure 5–20 shows the flowchart for the floating-point-to-integer conversion.

1 2 ... 141 142 143 144 145 146 147 148 149 150 151 ... 756 757

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