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,SH,RB
  10
  11 Pseudo-code:
  12
  13     n <- SH
  14     sum <- (RT) + (RA)
  15     diff <- (RT) - (RA)
  16     prod1 <- MULS(RB, sum)
  17     prod1_lo <- prod1[XLEN:(XLEN*2)-1]
  18     prod2 <- MULS(RB, diff)
  19     prod2_lo <- prod2[XLEN:(XLEN*2)-1]
  20     if n = 0 then
  21         RT <- prod1_lo
  22         RS <- prod2_lo
  23     else
  24         round <- [0]*XLEN
  25         round[XLEN -n] <- 1
  26         prod1_lo <- prod1_lo + round
  27         prod2_lo <- prod2_lo + round
  28         m <- MASK(n, (XLEN-1))
  29         res1 <- ROTL64(prod1_lo, XLEN-n) & m
  30         res2 <- ROTL64(prod2_lo, XLEN-n) & m
  31         signbit1 <- prod1_lo[0]
  32         signbit2 <- prod2_lo[0]
  33         smask1 <- ([signbit1]*XLEN) & ¬m
  34         smask2 <- ([signbit2]*XLEN) & ¬m
  35         RT <- (res1 | smask1)
  36         RS <- (res2 | smask2)
  37
  38 Special Registers Altered:
  39
  40     None
  41
  42 # [DRAFT] Integer Butterfly Multiply Add and Accumulate FFT/DCT
  43
  44 A-Form
  45
  46 * maddrs  RT,RA,SH,RB
  47
  48 Pseudo-code:
  49
  50     n <- SH
  51     prod <- MULS(RB, RA)
  52     prod_lo <- prod[XLEN:(XLEN*2)-1]
  53     if n = 0 then
  54         RT <- (RT) + prod_lo
  55     else
  56         res <- (RT) + prod_lo
  57         round <- [0]*XLEN
  58         round[XLEN -n] <- 1
  59         res <- res + round
  60         signbit <- res[0]
  61         m <- MASK(n, (XLEN-1))
  62         res <- ROTL64(res, XLEN-n) & m
  63         smask <- ([signbit]*XLEN) & ¬m
  64         RT <- (res | smask)
  65
  66 Special Registers Altered:
  67
  68     None
  69
  70 # [DRAFT] Integer Butterfly Multiply Subtract From FFT/DCT
  71
  72 A-Form
  73
  74 * msubrs  RT,RA,SH,RB
  75
  76 Pseudo-code:
  77
  78     n <- SH
  79     prod <- MULS(RB, RA)
  80     prod_lo <- prod[XLEN:(XLEN*2)-1]
  81     if n = 0 then
  82         RT <- (RT) - prod_lo
  83     else
  84         res <- (RT) - prod_lo
  85         round <- [0]*XLEN
  86         round[XLEN -n] <- 1
  87         res <- res + round
  88         signbit <- res[0]
  89         m <- MASK(n, (XLEN-1))
  90         res <- ROTL64(res, XLEN-n) & m
  91         smask <- ([signbit]*XLEN) & ¬m
  92         RT <- (res | smask)
  93
  94 Special Registers Altered:
  95
  96     None