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section 7 - Index of

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SUBL Shift Left and Subtract Accumulators SUBLOperation:Assembler Syntax:2* O-S ..... 0 (parallel move) SUBL SO (parallel move)Description: Subtract the source operand S from two times the destination operand 0and store the result in the destination accumulator. The destination operand 0 is arithmeticallyshifted one bit to the left, and a zero is shifted into the LS bit <strong>of</strong> 0 prior to thesubtraction operation. The carry bit is set correctly if the source operand does not overflowas a result <strong>of</strong> the left shift operation. The overflow bit may be set as a result <strong>of</strong> eitherthe shifting or subtraction operation (or both). This instruction is useful for efficient divideand decimation in time (OIT) FFT algorithms.Example:SUBL A,B Y:(R5+N5),R7 ;2*B-A ..... B, load R7, no R5 updateBefore ExecutionAfter ExecutionAI $00:004000:000000 AI $00:004000:000000BI $00:005000:000000 BI $00:006000:000000Explanation <strong>of</strong> Example: Prior to execution, the 56-bit A accumulator contains thevalue $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 accumulatorfrom two times the value in the B accumulator and stores the 56-bit result in the B accumulator.

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