Motorola DSP56000 Manual page 547

SUBL
Operation:
2 ∗ D–S
D (parallel move)
Description: Subtract the source operand S from two times the destination operand D
and store the result in the destination accumulator. The destination operand D is arith-
metically shifted one bit to the left, and a zero is shifted into the LS bit of D prior to the
subtraction operation. The carry bit is set correctly if the source operand does not over-
flow as a result of the left shift operation. The overflow bit may be set as a result of either
the shifting or subtraction operation (or both). This instruction is useful for efficient divide
and decimation in time (DIT) FFT algorithms.
Example:
:
SUBL A,B
:
Before Execution
A
$00:004000:000000
B
$00:005000:000000
Explanation of Example: Prior to execution, the 56-bit A accumulator contains the
value $00:004000:000000, and the 56-bit B accumulator contains the value
$00:005000:000000. The SUBL A,B instruction subtracts the value in the A accumulator
from two times the value in the B accumulator and stores the 56-bit result in the B accu-
mulator.
A - 278
INSTRUCTION DESCRIPTIONS
Shift Left and Subtract Accumulators
;2 ∗ B–A
Y:(R5+N5),R7
INSTRUCTION SET DETAILS
Assembler Syntax:
SUBL S,D (parallel move)
B, load R7, no R5 update
After Execution
A
$00:004000:000000
B
$00:006000:000000
SUBL
MOTOROLA