incrementing a hex number

[Eugene Onishi]

I'm trying to incrment BCD number, what's the best way to do this?
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This message was ported from CCS's old forum
Original Post ID: 12025

[Pete Smith]

:=I'm trying to incrment BCD number, what's the best way to do this?

If you're doing a lot with BCD numbers, it would be useful to have a hex2bcd and bcd2hex routine. To increment the number, you'd just convert the number back into hex/decimal, increment it, and then convert it back again.

Here's what I use...

This one takes a BCD number, and returns the decimal equivalent, ie passing it 10 (BCD, real value=13) will return 10.

int bcd(int input)
{
int temp,temp2;

temp=(input & 0x0f);
temp2=((input & 0xf0)/16);

temp+=temp2*10;

return(temp);
}

This one does the opposite. If you pass it 10 (decimal), it'll return 10 BCD (13).

int to_bcd(int input)
{
int temp,temp2;

temp=input \% 10;
temp2=input/ 10;

temp2=temp2*16;

temp2+=temp;

return(temp2);
}

HTH

Pete.
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This message was ported from CCS's old forum
Original Post ID: 12030

[R.J.Hamlett]

:=I'm trying to incrment BCD number, what's the best way to do this?

A lot depends on whether you are after the smallest code space, or the fastest speed. You can either code using the 'modulus' function (\%), which gives simple code, but can be fairly slow, or just do a normal increment, and then adapt if there was a wrap over (this is the approach used in some microprocessors). The same applies when converting to/from BCD, where the use of a look up table, can be quicker, but will be bulkier than simple arithmetic.
The code below is a standard set of routines using the latter approach (including the conversions). Someone else has allready posted code using the former approach.

const unsigned int conv[16] = {
0,10,20,30,40,50,60,70,80,90,90,90,90,90,90,90 };
#define fromBCD(x) ((x & 0xf)+conv[(x>>4)])

/* Generic routine to increment a BCD number stored in an unsigned INT */
int BCDINC(int val)
{
/* routine to increment a BCD number */
if ((val & 0xf)>8)
{
/* here there must be a wrap */
val=val+7;
}
else
val++;
return(val
}

/* BCD conversion sub */
unsigned int toBCD(unsigned int val)
{
int ctr;
for (ctr=0;ctr<10;ctr++)
{
if (val == conv[ctr])
return(ctr<<4);
else if (val < conv[ctr]) break;
}
--ctr;
return((val-conv[ctr])+(ctr<<4));
}
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This message was ported from CCS's old forum
Original Post ID: 12032