section 7 - Index of

SUBR Shift Right and Subtract Accumulators SUBROperation:0/2-S ~ D (parallel move)Assembler Syntax:SUBR S,D (parallel move)Description: Subtract the source operand S from one-half the destination operand 0and store the result in the destination accumulator. The destination operand 0 is arithmeticallyshifted one bit to the right while the MS bit of 0 is held constant prior to the subtractionoperation. In contrast to the SUBL instruction, the carry bit is always setcorrectly, and the overflow bit can only be set by the subtraction operation, and not byanoverflow due to the initial shifting operation. This instruction is useful for efficient divideand decimation in time (DIT) FFT algorithms.Example:SUBR B,A N5,Y:-(R5);Al2-B ~ A, update R5, save N5Before ExecutionA~I ____ $8_0_:00_o_00_0:2_4_68_A_C __ ~After ExecutionA~I ____ $_co_:o_oo_oo_o_:oo_o_oo_o __ ~B~I ____ $_oo_:o_oo_OO_O_:12_3_45_6 __ ~B~I ____ $_oo_:o_oo_OO_O_:12_3_45_6 __ ~Explanation of Example: Prior to execution, the 56-bit A accumulator contains thevalue $80:000000:2468AC, and the 56-bit B accumulator contains the value$00:000000:123456. The SUBR B,A instruction subtracts the value in the B accumulatorfrom one-half the value in the A accumulator and stores the 56-bit result in the A accumulator.