Motorola CPU32 Reference Manual page 217

III
TBLU
TBLUN
Table Lookup and Interpolate (Unsigned)
TBLU
TBLUN
Unsigned table entries range from 0 to 2n-1 where n is 8, 16, or 32 for byte, word, and long-word
tables, respectively. Unsigned and unrounded table results are zero extended.
Rounding of the result is optionally selected via the 'R' instruction field. If R
=
0 (TBLU), the
fractional portion is rounded according to the round-to-nearest algorithm. The rounding
procedure can be summarized by the following table.
Adjusted Difference Rounding
Fraction Adjustment
1
+0
n<2'
n>1
-2
+1
The adjusted difference is then added to the selected table entry. The rounded result is returned
in the destination data register, Ox. Only the portion of the register corresponding to the selected
size is affected.
BYTE
WORD
LONG
31
UNAFFECTED
UNAFFECTED
RESULT
24 23 16 15
UNAFFECTED
UNAFFECTED
RESULT
8 7
o
UNAFFECTED
RESULT
RESULT RESULT
RESULT RESULT
If R
=
1 (TABLUN), the result is returned in register Ox without rounding. If the size is byte, the
integer portion of the result is returned in Ox (15:8). The integer portion of a word result is stored
in Ox (23:8). The least significant 24 bits of a long result are stored in Ox (31 :8). Byte and word
results are zero extended to fill the entire 32-bit register.
BYTE
WORD
LONG
MOTOROLA
4-164
31
24 23 16 15 8 7
o
ZERO EXTENDED ZERO EXTENDED RESULT FRACTION
ZERO EXTENDED RESULT RESULT
FRACTION
RESULT RESULT RESULT FRACTION
NOTE
A long-word result contains only the least significant 24 bits of integer preCision.
INSTRUCTION SET CPU32 REFERENCE MANUAL