openpower/isafunctions/fpfromint.mdwn

   1 # A.3 FLoating-Point Convert from Integer Model
   2
   3 The following describes algorithmically the operation of the Floating
   4 Convert From Integer instructions.
   5
   6 <!-- Power ISA Book I Version 3.0B Section A.3 page 782 -->
   7
   8     def INT2FP(FR, cvt, RN):
   9         if cvt = "sint2double" then
  10             tgt_precision = "double-precision"
  11             sign       <- FR[0]
  12         if cvt = "sint2single" then
  13             tgt_precision <- "single-precision"
  14             sign       <- FR[0]
  15         if cvt = "uint2double" then
  16             tgt_precision <- "double-precision"
  17             sign       <- 0
  18         if cvt = "uint2single" then
  19             tgt_precision <- "single-precision"
  20             sign       <- 0
  21
  22         result = [0] * 64
  23         exp        <- 63
  24         frac[0:63] <- FR
  25
  26         if frac[0:63] = 0 then
  27             # Zero Operand
  28             FPSCR[FR] <- 0b00
  29             FPSCR[FI] <- 0b00
  30             FPSCR[FPRF] <- "+ zero"
  31         else
  32             if sign = 1 then frac[0:63] <- ¬frac[0:63] + 1
  33             # do the loop 0 times if FR = max negative 64-bit integer or
  34             #                     if FR = max unsigned 64-bit integer
  35             do while frac[0] = 0
  36                 frac[0:63] <- frac[1:63] || 0b0
  37                 exp <- exp - 1
  38             Round_Float( tgt_precision, sign, exp, frac0:63, RN )
  39             if sign = 0 then FPSCR[FPRF] <- "+normal number"
  40             if sign = 1 then FPSCR[FPRF] <- "-normal number"
  41             result[0]    <- sign
  42             result[1:11] <- exp + 1023     # exp + bias
  43             result[12:63] <- frac[1:52]
  44
  45         return result
  46