openpower/isa/msubrs.mdwn

   1 <!-- SVP64 Butterfly DCT Instructions here described are based on -->
   2
   3 <!-- PLEASE NOTE THESE ARE UNAPPROVED AND DRAFT, NOT SUBMITTED TO OPF ISA WG -->
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   5 # [DRAFT] Integer Butterfly Multiply Add and Accumulate FFT/DCT
   6
   7 A-Form
   8
   9 * msubrs  RT,RA,RB,SH
  10
  11 Pseudo-code:
  12
  13     n <- SH
  14     prod <- MULS(RB, RA)
  15     if n = 0 then
  16         prod_lo <- prod[XLEN:(XLEN*2) - 1]
  17         RT <- (RT) - prod_lo
  18     else
  19         res[0:XLEN*2-1] <- (EXTSXL((RT)[0], 1) || (RT)) - prod
  20         round <- [0]*XLEN*2
  21         round[XLEN*2 - n] <- 1
  22         res <- res + round
  23         RT <- res[XLEN - n:XLEN*2 - n -1]
  24
  25 Special Registers Altered:
  26
  27     None