section 7 - Index of

RND Round Accumulator RNDOperation:D+r -+ D (parallel move)Assembler Syntax:RND D (parallel move)Description: Round the 56-bit value in the specified destination operand D and store theresult in the MSP portion of the destination accumulator (A 1 or 81). This instruction usesa convergent rounding technique. The contribution of the LS bits of the result (AO and80) is rounded into the upper portion of the result (A 1 or 81) by adding a rounding constantto the LS bits of the result. The MSP portion of the destination accumulator containsthe rounded result which may be read out to the data buses.The value of the rounding constant added is determined by the scaling mode bits SO and51 in the system status register (SR). A "1" is added in the rounding position as shownbelow:RoundingRounding ConstantS1 SO Scaling Mode Position 55-25 24 23 22 21 - 00 0 No Scaling 23 0 .... 0 0 1 0 0 .... 00 Scale Down 24 0 .... 0 1 0 0 0 .... 00 Scale Up 22 0 .... 0 0 0 0 .... 0Normal or "standard" rounding consists of adding a rounding constant to a givennumber of L5 bits of a value to produce a rounded result. The rounding constantdepends on the scaling mode being used as previously shown. Unfortunately, whenusing a twos-complement data representation, this process introduces a positive bias inthe statistical distribution of the roundoff error.