Texas Instruments TMS320C3x 사용자 설명서

Floating-Point Conversion (IEEE Std. 754)

5-17

Data Formats and Floating-Point Operation

Example 5–4 shows the fast conversion from IEEE to ’C3x floating-point format.
It properly handles the general case when 0 < 

e < 255, and also handles 0s (that

is, 

e = 0 and f = 0). The other special cases (denormalized, infinity, and NaN)

are not treated and, if present, will give erroneous results.

The fast version of the IEEE-to ’C3x conversion routine was originally developed
by Keith Henry of Apollo Computer, Inc. The other routines were based on this
initial input.

Example 5–4. IEEE-to-TMS320C3x Conversion (Fast Version)

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TITLE IEEE TO TMS320C3x CONVERSION (FAST VERSION)

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SUBROUTINE FMIEEE

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FUNCTION: CONVERSION BETWEEN THE IEEE FORMAT AND THE

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TMS320C3x FLOATING-POINT FORMAT. THE NUMBER TO

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BE CONVERTED IS IN THE LOWER 32 BITS OF R0.

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THE RESULT IS STORED IN THE UPPER 32 BITS OF R0.

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UPON ENTERING THE ROUTINE, AR1 POINTS TO THE

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FOLLOWING TABLE:

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(0) 0xFF800000 <

– –

 AR1

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(1) 0xFF000000

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(2) 0x7F000000

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(3) 0x80000000

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(4) 0x81000000

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ARGUMENT

ASSIGNMENTS:

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ARGUMENT

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FUNCTION

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–––––––––––+–––––––––––––––––––––––––––––––––––––

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R0

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NUMBER TO BE CONVERTED

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AR1

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POINTER TO TABLE WITH CONSTANTS

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REGISTERS USED AS INPUT: R0, AR1

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REGISTERS MODIFIED: R0, R1

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REGISTER CONTAINING RESULT: R0

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