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    <p>strstr is hard to optimize because (a) \0-termination means you have to read every byte anyway, and (b) it has to be good on all the edge cases, too.</p> <p>With that said, you can beat standard strstr by a factor of 10, using SSE2 ops. I've noticed that gcc 4.4 uses these ops for strlen now, but not for the other string ops. More on how to use SSE2 registers for strlen, strchr, strpbrk, etc. at <a href="http://mischasan.wordpress.com" rel="nofollow">mischasan.wordpress.com</a>. Pardon my super-terse code layout.</p> <pre><code>#include &lt;emmintrin.h&gt; // Other standard #includes you can figure out... static inline unsigned under(unsigned x) { return (x - 1) &amp; ~x; } static inline __m128i xmfill(char b) { return _mm_set1_epi8(b); } static inline __m128i xmload(void const*p) { return _mm_load_si128((__m128i const*)p); } static inline unsigned xmatch(__m128i a, __m128i b) { return _mm_movemask_epi8(_mm_cmpeq_epi8(a, b)); } char const *sse_strstr(char const *tgt, char const *pat) { unsigned len = sse_strlen(pat); if (len == 0) return tgt; if (len == 1) return sse_strchr(tgt,*pat); __m128i x, zero = {}; __m128i p0 = _m_set1_epi8(pat[0]), p1 = _m_set1_epi8(pat[1]); uint16_t pair = *(uint16_t const*)pat; unsigned z, m, f = 15 &amp; (uintptr_t)tgt; char const* p; // Initial unaligned chunk of tgt: if (f) { z = xmatch(x = xmload(tgt - f), zero) &gt;&gt; f; m = under(z) &amp; ((xmatch(x,p0) &amp; (xmatch(x,p1) &gt;&gt; 1)) &gt;&gt; f); for (; m; m &amp;= m - 1) if (!memcmp((p = tgt+ffs(m)-1)+2, pat+2, len-2)) return p; if (z) return NULL; tgt += 16 - f; if (*(uint16_t const*)(tgt - 1) == pair &amp;&amp; !memcmp(tgt+1, pat+2, len-2)) return tgt - 1; } // 16-byte aligned chunks of tgt: while (!(z = xmatch(x = xmload(tgt), zero))) { m = xmatch(x,p0) &amp; (xmatch(x,p1) &gt;&gt; 1); for (; m; m &amp;= m - 1) if (!memcmp((p = tgt+ffs(m)-1)+2, pat+2, len-2)) return p; tgt += 16; if (*(uint16_t const*)(tgt - 1) == pair &amp;&amp; !memcmp(tgt+1, pat+2, len-2)) return tgt - 1; } // Final 0..15 bytes of tgt: m = under(z) &amp; xmatch(x,p0) &amp; (xmatch(x,p1) &gt;&gt; 1); for (; m; m &amp;= m - 1) if (!memcmp((p = tgt+ffs(m)-1)+2, pat+2, len-2)) return p; return NULL; } </code></pre>
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    1. POAn SSE Stdlib-esque Library?
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    1. USNecrolis
    1. USMischa
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      1. VTUpMod
    1. COLLVM has a very nice vectorized `strstr` for skipping block comments(it has branches for msvc, gcc and altivec, so its pretty portable too). Thanks for the link though, i'll have a look
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      1. USNecrolis
    2. COThis is so outdated. Current glibc has SSE 4.2 optimization where available, which contains exactly the instructions needed for fast string operations.
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      1. USGunther Piez
    3. COWhich version of glibc is that? I agree that it's best when glibc does the lifting and arch-deps. Unfortunately, it's a problem that SSE4.2 is intel-only, while pretty much ANY intel-compatible chip since 2003 has SSE2. For non-(intel SSE4.2) platforms, my glibc strstr doesn't seem to be quite so smart :-(
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