openpower/isa/maddsubrs.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 Round Shift for FFT/DCT
   6
   7 A-Form
   8
   9 * maddsubrs  RT,RA,RB,SH
  10
  11 Pseudo-code:
  12
  13     n <- SH
  14     sum <- (RT[0] || RT) + (RA[0] || RA)
  15     diff <- (RT[0] || RT) - (RA[0] || RA)
  16     prod1 <- MULS(RB, sum)
  17     prod2 <- MULS(RB, diff)
  18     if n = 0 then
  19         prod1_lo <- prod1[XLEN+1:(XLEN*2)]
  20         prod2_lo <- prod2[XLEN+1:(XLEN*2)]
  21         RT <- prod1_lo
  22         RS <- prod2_lo
  23     else
  24         round <- [0]*(XLEN*2 + 1)
  25         round[XLEN*2 - n + 1] <- 1
  26         prod1 <- prod1 + round
  27         prod2 <- prod2 + round
  28         res1 <- prod1[XLEN - n + 1:XLEN*2 - n]
  29         res2 <- prod2[XLEN - n + 1:XLEN*2 - n]
  30         RT <- res1
  31         RS <- res2
  32
  33 Special Registers Altered:
  34
  35     None