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POWhat's the most efficient way to compare two blocks of memory in the D language?
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copied!<p>I need a comparison function for blocks of memory for doing binary searches on arrays of bytes in the D programming language. It does not need to have any useful semantics. It only needs to be fast and be a valid comparison function (one that produces a total ordering). The blocks of memory to be compared are already known to be the same length.</p> <p>C's <code>memcmp</code> is actually pretty slow because it tries to preserve useful string comparison semantics, which I don't need. Below is the best I've come up with so far. Does anyone know of anything better, preferably w/o dipping into non-portable CPU-specific instructions?</p> <pre><code>// Faster than C's memcmp because it doesn't preserve any meaningful // semantics. It's just a completely arbitrary, but really fast, // comparison function. int memoryCompare(const(void)* lhs, const(void)* rhs, size_t n) { for(; n >= uint.sizeof; n -= uint.sizeof) { if( *(cast(uint*) lhs) < *(cast(uint*) rhs)) { return -1; } else if( *(cast(uint*) lhs) > *(cast(uint*) rhs)) { return 1; } lhs += uint.sizeof; rhs += uint.sizeof; } for(; n >= ubyte.sizeof; n -= ubyte.sizeof) { if( *(cast(ubyte*) lhs) < *(cast(ubyte*) rhs)) { return -1; } else if( *(cast(ubyte*) lhs) > *(cast(ubyte*) rhs)) { return 1; } lhs += ubyte.sizeof; rhs += ubyte.sizeof; } return 0; } </code></pre> <p>Edit: I've read up on SSE and I don't want to use it for 3 reasons:</p> <ol> <li>It's not portable.</li> <li>It requires programming in ASM.</li> <li>The comparison instructions assume your data is floating points, which might be problematic if some data happens to match the pattern for a NaN.</li> </ol>

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