Re: fscanf performance > 10x slower in 2.1.69 compared to 2.1.50 on Windows

I did some investigating as to the source of this problem, and have 
determined that the stream inserter for floating point numbers is quite 
slow.  This accounts for about 2/3s of the time. About 10% of the time is 
spent extracting and replacing characters to handle NA, Nan, and Inf 
entries.

The following code is about 3x faster (slower than before, but perhaps 
acceptable). It replaces the "octave_scan" template specialization for 
double* in oct-stream.cc.

#define TMP_FP_BUFSIZE 128
template <>
std::istream&
octave_scan (std::istream& is, const scanf_format_elt& fmt, double* valptr)
{
 double& ref = *valptr;

 char buf[TMP_FP_BUFSIZE];
 switch (fmt.type)
   {
   case 'e':
   case 'f':
   case 'g':
     {
       is.width(TMP_FP_BUFSIZE-1);    // Protect image against strange file
       buf[TMP_FP_BUFSIZE-2] = 0;     // Zero char sentinel
       is >> buf;
       if (is && buf[TMP_FP_BUFSIZE-2]==0) // Not eof, and field wasn't 
gigantic
         {
           if (isdigit(buf[0])  || buf[0]=='+'  || buf[0] == '-' || 
buf[0]=='.')
             {
               ref =  atof(buf);
             }
           else if (strcmp(buf, "NA")==0)
             {
               ref = octave_NA;
             }
           else if (strcmp(buf, "NaN")==0)
             {
               ref = octave_NaN;
             }
           else if (strcmp(buf, "Inf") == 0)
             {
               ref = octave_Inf;
             }
           else {
               is.setstate(std::ios_base::failbit);
            }
          }
       else {  // Unparsable number (too long).  Set fail and quit
           if (buf[TMP_FP_BUFSIZE-2]==0) 
is.setstate(std::ios_base::failbit);
       }
       break;
     }
   default:
     panic_impossible ();
     break;
   }
 return is;
} 



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