Re: [boost] lexical_cast optimization

Subject: Re: [boost] lexical_cast optimization
From: Jonathan Brannan (kickace_at_[hidden])
Date: 2008-12-05 10:40:13

we have found that atoi/strtol/strtoll/strtod are slow compared to the
optimized output (gcc -O2/3) of a very simple * 10 loop.  The C number
converters work for a large varity of bases, which makes them slower
than needed for base 10.

we use something like:

  template<typename TInteger>
    bool validated_to_unsigned_int(
        const char* str_value, size_t size,
        TInteger& result)
    {
      size_t i = 0;
      for(const char* p = str_value; i < size; ++p, ++i)
      {
        char digit = *p;
        if (digit >= '0' && digit <='9')
        {
          result = result * 10 + digit - '0';
        }
        else
        {
          return false;
        }
      }
      return true;
    }

with wrappers for signed and ones that throw exceptions.  We have a
few converters that are faster, but only without error checking (base
16 conversion with lookup table works for small numbers, for example)