openpower/isafunctions/roundfloat.mdwn

   1 # A.3 Round to Float conversion
   2
   3 <!-- Power ISA Book I Version 3.0B Section A.3 page 782 -->
   4
   5     def Round_Float( tgt_precision, sign, exp, frac, round_mode ):
   6        inc <- 0
   7        if tgt_precision = "single-precision" then
   8            lsb <- frac[23]
   9            gbit <- frac[24]
  10            rbit <- frac[25]
  11            xbit <- frac[26:63] > 0
  12         else # tgt_precision = "double-precision"
  13             lsb  <= frac[52]
  14             gbit <= frac[53]
  15             rbit <= frac[54]
  16             xbit <= frac[55:63] > 0
  17
  18         if round_mode  = 0b00  then           # Round to Nearest
  19             if lsb = 1 and gbit = 1              then inc <- 1
  20             if lsb = 0 and gbit = 1 and rbit = 1 then inc <- 1
  21             if lsb = 0 and gbit = 1 and xbit = 1 then inc <- 1
  22         end
  23         if round_mode  = 0b10  then           # Round toward + Infinity
  24             if sign = 0 and gbit = 1 then inc <-1
  25             if sign = 0 and rbit = 1 then inc <-1
  26             if sign = 0 and xbit = 1 then inc <-1
  27         end
  28         if round_mode  = 0b11  then           # Round toward - Infinity
  29             if sign = 1 and gbit = 1 then inc <-1
  30             if sign = 1 and rbit = 1 then inc <-1
  31             if sign = 1 and xbit = 1 then inc <-1
  32         end
  33         if tgt_precision = "single-precision" then
  34             frac[0:23] <- frac[0:23] + inc
  35         else # tgt_precision = "double-precision"
  36             frac[0:52] <- frac[0:52] + inc
  37         if carry_out = 1 then exp <- exp + 1
  38         FPSCR[FR] <- inc
  39         FPSCR[FI] <- gbit | rbit | xbit
  40         FPSCR[XX] <- FPSCR[XX] | FPSCR[FI]
  41