Question

How do I convert binary data to hex value in obj-c?
Example:

1111 = F, 
1110 = E, 
0001 = 1, 
0011 = 3.

I have a NSString of 10010101010011110110110011010111, and i want to convert it to hex value.
Currently I’m doing in a manual way. Which is,

-(NSString*)convertToHex:(NSString*)hexString

{
NSMutableString *convertingString = [[NSMutableString alloc] init];

for (int x = 0; x < ([hexString length]/4); x++) {

    int a = 0;
    int b = 0; 
    int c = 0;
    int d = 0;

    NSString *A = [NSString stringWithFormat:@"%c", [hexString characterAtIndex:(x)]];
    NSString *B = [NSString stringWithFormat:@"%c", [hexString characterAtIndex:(x*4+1)]];
    NSString *C = [NSString stringWithFormat:@"%c", [hexString characterAtIndex:(x*4+2)]];
    NSString *D = [NSString stringWithFormat:@"%c", [hexString characterAtIndex:(x*4+3)]];


    if ([A isEqualToString:@"1"]) { a = 8;}

    if ([B isEqualToString:@"1"]) { b = 4;}

    if ([C isEqualToString:@"1"]) { c = 2;}

    if ([D isEqualToString:@"1"]) { d = 1;}

    int total = a + b + c + d;

    if (total < 10) { [convertingString appendFormat:@"%i",total]; }
    else if (total == 10) { [convertingString appendString:@"A"]; }
    else if (total == 11) { [convertingString appendString:@"B"]; }
    else if (total == 12) { [convertingString appendString:@"C"]; }
    else if (total == 13) { [convertingString appendString:@"D"]; }
    else if (total == 14) { [convertingString appendString:@"E"]; }  
    else if (total == 15) { [convertingString appendString:@"F"]; } 

}

NSString *convertedHexString = convertingString;
return [convertedHexString autorelease];
[convertingString release];

}

Anyone have better suggestion? This is taking too long.
Thanks in advance.

Answer 1

I have never been much of a C hacker myself, but a problem like this is perfect for C, so here is my modest proposal – coded as test code to run on the Mac, but you should be able to copy the relevant bits out to use under iOS:

#import <Foundation/Foundation.h>

int main(int argc, char *argv[]) {
    NSAutoreleasePool *p = [[NSAutoreleasePool alloc] init];

    NSString *str = @"10010101010011110110110011010111";

    char* cstr = [str cStringUsingEncoding: NSASCIIStringEncoding];

    NSUInteger len = strlen(cstr);

    char* lastChar = cstr + len - 1;
    NSUInteger curVal = 1;

    NSUInteger result = 0;

    while (lastChar >= cstr) {

        if (*lastChar == '1')
        {
            result += curVal;
        }
        /*
        else 
        {
            // Optionally add checks for correct characters here
        }
        */

        lastChar--;
        curVal <<= 1;
    }

    NSString *resultStr = [NSString stringWithFormat: @"%x", result];

    NSLog(@"Result: %@", resultStr);

    [p release];
}

It seems to work, but I am sure that there is still room for improvement.