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Manipulate two 8-Bits using Carry?

 
 
Bryan Parkoff
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      09-06-2005
I break one U_WORD variable into two U_BYTE variables. I prefer to
manipulate two U_BYTE variables instead of one U_WORD variable using Carry.
Please look at my example using U_WORD variable below.

typedef unsigned char U_BYTE;
typedef unsigned short int U_WORD;

U_WORD HighLow = 0x00FE;
HighLow += 0x04;
U_BYTE Carry = HighLow >> 8;

It is not what I want to use this above. Please look at my example
using two U_BYTE variables below.

typedef unsigned char U_BYTE;

U_BYTE Low = 0xFE;
U_BYTE High = 0x00;
U_BYTE Carry = 0x00;
U_BYTE Temp = Low;
Low += 0x04;

if (Temp <= Low)
Carry = 0x00;
else
{
Carry = 0x01;
High += Carry;
}

My code above works fine. It is what I am using. It always use
unsigned when Low increases. If it wraps to 0, it sets Carry to increase
High. How can I write signed code? It has to tell Low to decrease using
signed. If it wraps to 0xFF, it sets Carry to decrease High. Low must
always use "+" to support unsigned and signed. For example below.

typedef unsigned short int U_WORD;
typedef signed short int S_WORD;

U_WORD HighLow = 0x0002;
HighLow += (S_WORD) 0xFC; // It shows 0xFFFE
U_BYTE Carry = (HighLow >> & 0x01; // It captures 0xFF to mask 0x01.

Can you please write two U_BYTE variables using signed in an example
code?


Bryan Parkoff


 
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