Question

In one of my C application I am using, below functions from ctype.h :

isalpha(), isspace(), ispunct(), tolower().

After profiling I see there are some bottlenecks in the calls of these functions(Basically my app is a character/string processing from a input text file and hence these functions are called exhaustively inside critical loops)I want to optimize them for speed and have my own implementation if it helps.

Where can I find such or logic to implement them?

Answer 1

It sounds to me odd that such functions can be your bottleneck; likely they can take into account the locale, and this makes them “slower”. If you can disregard it, then you can implement them as easily as (e.g.: this is just an idea wrote on the fly)

bool isalpha(int c)
{
   return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
}

bool isspace(int c)
{
   return c == ' ' || c == '\t'; // || whatever other char you consider space
}

bool ispunct(int c)
{
   static const char *punct = ".;!?...";
   return strchr(punct, c) == NULL ? false : true; // you can make this shorter
}

int tolower(int c)
{
   if ( !isalpha(c) ) return c;
   return (c >= 'A' && c <= 'Z') ? c - 'A' : c;
}

Then make them inline functions.