openpower/isa/butterfly.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 -->
   4
   5 # [DRAFT] Integer Butterfly Multiply Add/Sub FFT/DCT
   6
   7 DCTI-Form
   8
   9 * maddsubrs  RT,RA,RB,SH
  10
  11 Pseudo-code:
  12
  13     sum <- (RT) + (RA)
  14     diff <- (RT) - (RA)
  15     prod1 <- MUL(RB, sum)
  16     prod2 <- MUL(RB, diff)
  17     res1 <- ROTL64(prod1, XLEN-SH)
  18     res2 <- ROTL64(prod2, XLEN-SH)
  19     RT <- (RT) + res1
  20     RS <- (RS) + res2
  21
  22 Special Registers Altered:
  23
  24     None