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copied!<p><em>liw.fi</em> is right, by the way. I was a bit surprised by this, since strcspn has to do a much more general problem than the isdigit() approach, but it seems to be the case:</p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <string.h> #include <ctype.h> #include <assert.h> #define NTESTS 10000 #define TESTSIZE 10000 char stest1[TESTSIZE]; char stest2[TESTSIZE]; int test_isdigit(char *s) { while (*s) { if (isdigit(*s)) return 1; s++; } return 0; } int test_range(char *s) { while (*s) { if ((*s >= '0') && (*s <= '9')) return 1; s++; } return 0; } int test_strcspn(char *s) { return s[strcspn(s, "0123456789")] != '\0'; } int main(int argc, char **argv) { long int i; for (i=0; i<TESTSIZE; i++) { stest1[i] = stest2[i] = 'A' + i % 26; } stest2[TESTSIZE-1] = '5'; int alg = atoi(argv[1]); switch (alg) { case 0: printf("Testing strcspn\n"); for (i=0; i<NTESTS; i++) { assert(test_strcspn(stest1) == 0); assert(test_strcspn(stest2) != 0); } break; case 1: printf("Testing isdigit() loop\n"); for (i=0; i<NTESTS; i++) { assert(test_isdigit(stest1) == 0); assert(test_isdigit(stest2) != 0); } break; case 2: printf("Testing <= => loop\n"); for (i=0; i<NTESTS; i++) { assert(test_range(stest1) == 0); assert(test_range(stest2) != 0); } break; default: printf("eh?\n"); exit(1); } return 0; } </code></pre> <p>It's awfully hard to beat the standard libraries at their own game ... (the usual caveats apply -- YMMV)</p> <pre><code>$ gcc -O6 -Wall -o strcspn strcspn.c $ time ./strcspn 0 Testing strcspn real 0m0.085s user 0m0.090s sys 0m0.000s $ time ./strcspn 1 Testing isdigit() loop real 0m0.753s user 0m0.750s sys 0m0.000s $ time ./strcspn 2 Testing <= => loop real 0m0.247s user 0m0.250s sys 0m0.000s </code></pre> <hr> <p>UPDATE: Just for fun, I added a bitmap lookup version based on Mike Dunlavey's answer:</p> <pre><code>char bitmap[256] = { /* 0x00 */ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x10 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x20 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* 0x30 */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, }; int test_bitmap(char *s) { while (!bitmap[*(unsigned char *)s]) s++; return (*s); } </code></pre> <p>Which slightly outperforms the others (~.170s) but still can't touch strcspn!</p>

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