openpower/isa/bcd.mdwn

   1 <!-- Instructions here described in PowerISA Version 3.0 B Book 1 -->
   2
   3 <!-- Section 3.3.15 Binary Coded Decimal (BCD) Assist Instructions. Page 111 -->
   4
   5 <!-- The Binary Coded Decimal Assist instructions operate on Binary Coded Decimal -->
   6 <!-- operands (cbcdtd and addg6s) and Decimal Floating-Point operands (cdtbcd) -->
   7 <!-- See Chapter 5. for additional information. -->
   8
   9
  10 # Convert Declets To Binary Coded Decimal
  11
  12 X-Form
  13
  14 * cdtbcd RA,RS
  15
  16 Pseudo-code:
  17
  18     src <- [0]*64
  19     src[64-XLEN:63] <- (RS)
  20     result <- [0]*64
  21     do i = 0 to 1
  22       n <- i * 32
  23       result[n+0:n+7] <- 0
  24       result[n+8:n+19] <- DPD_TO_BCD(src[n+12:n+21])
  25       result[n+20:n+31] <- DPD_TO_BCD(src[n+22:n+31])
  26     RA <- result[64-XLEN:63]
  27
  28 Special Registers Altered:
  29
  30     None
  31
  32 # Add and Generate Sixes
  33
  34 XO-Form
  35
  36 * addg6s RT,RA,RB
  37
  38 Pseudo-code:
  39
  40     sum <- (0b0000 || (RA)) + (0b0000 || (RB))
  41     carries <- sum ^ (0b0000 || (RA)) ^ (0b0000 || (RB))
  42     ones <- [0b0001] * (XLEN / 4)
  43     nibbles_need_sixes <- ¬carries[0:XLEN-1] & ones
  44     RT <- nibbles_need_sixes * 0b0110
  45
  46 Special Registers Altered:
  47
  48     None
  49
  50 # Convert Binary Coded Decimal To Declets
  51
  52 X-Form
  53
  54 * cbcdtd RA,RS
  55
  56 Pseudo-code:
  57
  58     src <- [0]*64
  59     src[64-XLEN:63] <- (RS)
  60     result <- [0]*64
  61     do i = 0 to 1
  62       n <- i * 32
  63       result[n+0:n+11] <- 0
  64       result[n+12:n+21] <- BCD_TO_DPD(src[n+8:n+19])
  65       result[n+22:n+31] <- BCD_TO_DPD(src[n+20:n+31])
  66     RA <- result[64-XLEN:63]
  67
  68 Special Registers Altered:
  69
  70     None
  71
  72 <!-- Checked March 2021 -->