<!-- Instructions here described in PowerISA Version 3.0 B Book 1 -->

<!-- Section 3.3.15 Binary Coded Decimal (BCD) Assist Instructions. Page 111 -->

<!-- The Binary Coded Decimal Assist instructions operate on Binary Coded Decimal -->
<!-- operands (cbcdtd and addg6s) and Decimal Floating-Point operands (cdtbcd) -->
<!-- See Chapter 5. for additional information. -->


# Convert Declets To Binary Coded Decimal

X-Form

* cdtbcd RA,RS

Pseudo-code:

    src <- [0]*64
    src[64-XLEN:63] <- (RS)
    result <- [0]*64
    do i = 0 to 1
      n <- i * 32
      result[n+0:n+7] <- 0
      result[n+8:n+19] <- DPD_TO_BCD(src[n+12:n+21])
      result[n+20:n+31] <- DPD_TO_BCD(src[n+22:n+31])
    RA <- result[64-XLEN:63]

Special Registers Altered:

    None

# Add and Generate Sixes

XO-Form

* addg6s RT,RA,RB

Pseudo-code:

    sum <- (0b0000 || (RA)) + (0b0000 || (RB))
    carries <- sum ^ (0b0000 || (RA)) ^ (0b0000 || (RB))
    ones <- [0b0001] * (XLEN / 4)
    nibbles_need_sixes <- ¬carries[0:XLEN-1] & ones
    RT <- nibbles_need_sixes * 0b0110

Special Registers Altered:

    None

# Convert Binary Coded Decimal To Declets

X-Form

* cbcdtd RA,RS

Pseudo-code:

    src <- [0]*64
    src[64-XLEN:63] <- (RS)
    result <- [0]*64
    do i = 0 to 1
      n <- i * 32
      result[n+0:n+11] <- 0
      result[n+12:n+21] <- BCD_TO_DPD(src[n+8:n+19])
      result[n+22:n+31] <- BCD_TO_DPD(src[n+20:n+31])
    RA <- result[64-XLEN:63]

Special Registers Altered:

    None

<!-- Checked March 2021 -->