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 A-Form
   8
   9 * maddsubrs  RT,RA,RB,SH
  10
  11 Pseudo-code:
  12
  13     n <- XLEN-SH
  14     sum <- (RT) + (RA)
  15     diff <- (RT) - (RA)
  16     prod1[0:(XLEN*2)-1] <- MULS(RB, sum)
  17     prod2[0:(XLEN*2)-1] <- MULS(RB, diff)
  18     res1 <- prod1[XLEN/2-SH:XLEN-1-SH]
  19     res2 <- prod2[XLEN/2-SH:XLEN-1-SH]
  20     RT <- (RT) + EXTS(res1)
  21     RS <- (RS) + EXTS(res2)
  22
  23 Special Registers Altered:
  24
  25     None