Typewriter User Manual

MOTOROLA MC68340 USER’S MANUAL 5- 35

First, the results of each TBL are rounded with the TBLS round-to-nearest-even algorithm.

The following values would be returned by TBLS:

TBL # 1 0010 0000 .

TBL # 2 0011 1111 .

TBL # 3 0000 0001 .

Summing, the following result is obtained:

0010 0000 .

0011 1111 .

0000 0001 .

0110 0000 .

Now, using the same TBL results, the sum is first calculated and then rounded according

to the same algorithm:

0010 0000 . 0111 0000

0011 1111 . 0111 0000

0000 0001 . 0111 0000

0110 0001 . 0101 0000

Rounding yields:

0110 0001 .

The second result is preferred. The following code sequence illustrates how addition of a

series of table interpolations can be performed without loss of precision in the intermediate

results:

L0:

TBLSN.B 〈ea〉, Dx

TBLSN.B 〈ea〉, Dl

ADD.L Dx, Dm Long addition avoids problems with carry

ADD.L Dm, Dl

ASR.L #8, Dl Move radix point

BCC.B L1 Fraction MSB in carry

ADDQ.B #1, Dl

L1: . . .

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

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