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Will Reeve
Joined: 30 Oct 2003
Posts: 209
Location: Norfolk, England
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| reverse sprintf! |
 Posted: Wed Oct 11, 2006 4:02 am |
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Hi,
I thought I would cheat and ask here before I go off and code something. I remember seeing some code posted a few years ago which did this but can't find it in a search. Anyway.
I have two bytes which represent a hex "word" in ASCII. i.e. type bytes 'F' 'E' and I want to convert this to a int8 variable set to 254.
I am sure there is a easy way to do this?
Keep well,
Will |
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Ttelmah
Guest
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| Posted: Wed Oct 11, 2006 5:02 am |
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There have been some published partial 'sscanf' functions, but for a single simple conversion like this, DIY, will be a lot smaller and faster.
The conversion is very simple. If the characters are in an array then:
| Code: |
#define valhex(x) (x<':')?(x-'0'):(x-'7')
int8 hex_to_bin(char * digits) {
return (valhex(digits[0])<<4)+(valhex(digits[1]);
}
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Call this with the address of the first hex digit.
This will only handle upper case hex. A more generic form, would test/handle the lower case version as well.
There may have been a published version of 'HexToBin' (which is the standard C version of this function), but I can't spot one at present.
Best Wishes |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Wed Oct 11, 2006 8:14 am |
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Here is my implementation of atoi(). A bit more difficult to
understand because highly optimized for compact code size.
This implementation is case insensitive.
| Code: | #include <18F458.H>
#fuses HS, NOWDT, PUT, NOLVP
#use delay(clock=16000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//--------------------------------------------------------
// Convert a hexadecimal string to an unsigned 8 bit integer.
//
// Note that this function requires the string to have a length
// of two characters. A zero termination of the string is
// optional.
// Both lowercase and uppercase characters are accepted.
//--------------------------------------------------------
int8 atoi8(char *string)
{
int8 result=0;
int8 i=2;
int8 digit;
do
{
result <<= 4;
digit = (*string);
result += (digit & 0x0F);
if (digit >= 'A')
result += 9;
string++;
} while (--i);
return result;
}
//==============================
void main(void)
{
char buffer[3] = {"0A"};
int8 result;
result = atoi8(buffer);
printf("result = %u \n\r", result);
while(1);
} |
Edit 11-Oct-2006: Fixed two bugs in the conversion and added example code. Thanks PCM. |
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