Date: Tue, 21 Apr 2015 17:52:23 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 199587] libc strncmp() performance Message-ID: <bug-199587-8@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199587 Bug ID: 199587 Summary: libc strncmp() performance Product: Base System Version: 10.1-STABLE Hardware: Any OS: Any Status: New Severity: Affects Many People Priority: --- Component: misc Assignee: freebsd-bugs@FreeBSD.org Reporter: blackngel1@gmail.com I've been tinkering with the code, out of curiosity, and I've reimplemented strncmp() to check the performance. Here are my results and the benchmark code: 42359800221 cycles -- FreeBSD strncmp() 42113090043 cycles -- FreeBSD strncmp() 42145558182 cycles -- FreeBSD strncmp() 39479522958 cycles -- My Implementation 39447595998 cycles -- My Implementation 39445708599 cycles -- My Implementation My implementation always runs a bit faster and seems more clean. -------------- #include <stdio.h> unsigned long long rdtsc(void) { unsigned int low, hi; __asm__ volatile( "rdtsc\n" : "=a"(low), "=d"(hi) : : "memory"); return ((unsigned long long)hi << 32) | (unsigned long long) low; } int strncmpnew(const char *p, const char *q, size_t n) { while (n > 0 && *p && (*p == *q)) n--, p++, q++; return (n == 0) ? 0: ((const unsigned char)*p - (const unsigned char)*q); } int strncmpfbsd(const char *s1, const char *s2, size_t n) { if (n == 0) return (0); do { if (*s1 != *s2++) return (*(const unsigned char *)s1 - *(const unsigned char *)(s2 - 1)); if (*s1++ == '\0') break; } while (--n != 0); return (0); } void test(int (*f)(const char *, const char *, unsigned int n), unsigned int iters, char *msg) { char *str1 = "abcdefghijklmnopqrstuvwxyz0123456789A"; char *str2 = "abcdefghijklmnopqrstuvwxyz0123456789A"; unsigned long foo = 0; unsigned long long int st = rdtsc(); unsigned int i; for (i = 0; i < iters; i++) foo += f(str1, str2, 37); unsigned long long int tot = rdtsc() - st; printf("%20llu cycles -- %s\n", tot, msg); asm volatile( "" :: "g"(foo) : "memory"); } int main(void) { unsigned int iters = 100000000; test(strncmpfbsd, iters, "FreeBSD strncmp()"); test(strncmpfbsd, iters, "FreeBSD strncmp()"); test(strncmpfbsd, iters, "FreeBSD strncmp()"); test(strncmpnew, iters, "My Implementation"); test(strncmpnew, iters, "My Implementation"); test(strncmpnew, iters, "My Implementation"); getchar(); return 0; } -------------- -- You are receiving this mail because: You are the assignee for the bug.
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