A quick way to count the number of newlines '/n' in string of 200 chars

Question

I am trying to establish the number of lines that a string will generate.
I can do this by counting the number of '/n' in the string. However my brute force method (shown below) is very slow.
Normally this would not be a problem on a 2800mhz Athlon (Standard) PC this takes < 1 second. However this code resides within a speed critical loop (not shown). The code shown below is a Achilles heal as far as the performance of this speed critical loop goes.
Can anyone suggest a faster way to count the number of �/n� (new lines) within a text string of around 50- 1000 chars, given that there may be 10 � 100 newline chars. Speed is a very important factor for this part of my program.
Thanks in advance
Andrew.
    int lineCount =0;
    String txt = this.getText();
    //loop throught text and count the carridge returns
    for (int i = 0; i < txt.length(); i++)
      char ch = txt.charAt(i);
      if (ch == '\n')
       lineCount ++;
    }//end forMessage was edited by:
scottie_uk
Message was edited by:
scottie_uk

Answer 1

Well, here is a C version. On my computer the Java version (reply 9 above) is slightly faster than C. YMMV. For stuff like this a compiler can be hard to beat even with assembler, as you need to do manual loop unrolling and method inlining which turn assembly into a maintenance nightmare.
// gcc -O6 -fomit-frame-pointer -funroll-loops -finline -o newlines.exe newlines.c
#include <stdio.h>
#include <string.h>
#if defined(__GNUC__) || defined(__unix__)
#include <time.h>
#include <sys/time.h>
#else
#include <windows.h>
#endif
#if defined(__GNUC__) || defined(__unix__)
typedef struct timeval TIMESTAMP;
void currentTime(struct timeval *time)
    gettimeofday(time, NULL);
int milliseconds(struct timeval *start, struct timeval *end)
    int usec = (end->tv_sec - start->tv_sec) * 1000000 +
     end->tv_usec - start->tv_usec;
    return (usec + 500) / 1000;
#else
typedef FILETIME TIMESTAMP;
void currentTime(FILETIME *time)
    GetSystemTimeAsFileTime(time);
int milliseconds(FILETIME *start, FILETIME *end)
    int usec = (end->dwHighDateTime - start->dwHighDateTime) * 1000000L +
     end->dwLowDateTime - start->dwLowDateTime;
    return (usec + 500) / 1000;
#endif
static int count(register char *txt)
    register int count = 0;
    register int c;
    while (c = *txt++)
     if (c == '\n')
         count++;
    return count;
static void doit(char *str)
    TIMESTAMP start, end;
    long time;
    register int n;
    int total = 0;
    currentTime(&start);
    for (n = 0; n < 1000000; n++)
     total += count(str);
    currentTime(&end);
    time = milliseconds(&start, &end);
    total *= 4;
    printf("time %ld, total %d\n", time, total);
    fflush(stdout);
int main(int argc, char **argv)
    char buf[1024];
    int n;
    for (n = 0; n < 256 / 4; n++)
     strcat(buf, "abc\n");
    for (n = 0; n < 5; n++)
     doit(buf);
}