Arithmetic with binary-coded decimal (BCD)

[odometer]

I was thinking about binary-coded decimal, and here is something I found when googling "BCD arithmetic":
http://www.divms.uiowa.edu/~jones/bcd/bcd.html

I am not quite sure how to (mathematically) prove that some of them work, though. But I can still play with them.

Here is my own contribution (untested):

Code: Select all

half(a)
   t1 = a >> 1
   t2 = t1 & 0x08888888
   t3 = (t2 >> 2) | (t2 >> 3)
   return t1 - t3


[Zener]

How many bits is t2?

[odometer]

How many bits is t2?

These are all 32-bit variables. Please see the link; this piece of pseudocode here is in the same format as the ones on the linked page.

[Len17]

In the good old days, the compiler automatically did arithmetic on BCD variables using the CPU's BCD arithmetic instructions.

[mtbf0]

In the good old days, the compiler automatically did arithmetic on BCD variables using the CPU's BCD arithmetic instructions.

risc fixed that.