hexdec.m

#import <Foundation/Foundation.h>

// Adapted from http://stackoverflow.com/a/11068850
/** 
 * @brief convert a hexidecimal string to a signed long
 * will not produce or process negative numbers except 
 * to signal error.
 * 
 * @param hex without decoration, case insensative. 
 * 
 * @return -1 on error, or result (max sizeof(long)-1 bits)
 */
long hexdec(const char *hex, int len)
    {
    #pragma clang diagnostic push
    #pragma clang diagnostic ignored "-Winitializer-overrides"
    static const int hextable[] = {
       [0 ... 255] = -1,                     // bit aligned access into this table is considerably
       ['0'] = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, // faster for most modern processors,
       ['A'] = 10, 11, 12, 13, 14, 15,       // for the space conscious, reduce to
       ['a'] = 10, 11, 12, 13, 14, 15        // signed char.
    };
    #pragma clang diagnostic pop

    int ret = 0;
    if (len > 0)
        {
        while (*hex && ret >= 0 && (len--))
            {
            ret = (ret << 4) | hextable[*hex++];
            }
        }
    else
        {
        while (*hex && ret >= 0)
            {
            ret = (ret << 4) | hextable[*hex++];
            }
        }
    return ret; 
    }

int main(int argc, char *argv[])
    {
    @autoreleasepool
        {
        int d = hexdec("DEADBEEF", 4);
        NSLog(@"%d 0x%X", d, d);
        d = hexdec("DEADBEEF", 0);
        NSLog(@"%d 0x%X", d, d);
        }
    }