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    <p>How about:</p> <pre><code>int foo(int x,int y) { // As suggested by Luther Blissett below in the comments. // Increased the size of the array to 16x16. // This allows for simpler optimization for the compiler // Also use +8 rather +6 in the hopes that compiler optimization will be easier // you never know (there may be some fancy trick. static int sign[16][16] = { { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 1, 1, 1, 1, 1, 1, 1, 1, 0, -1, -1, -1, -1, -1, -1, -1}, { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 1, 1, 1, 1, 1, 1}, { -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 1, 1, 1, 1, 1, 1}, { -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 1, 1, 1, 1, 1, 1}, { -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 1, 1, 1, 1, 1, 1}, { -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 1, 1, 1, 1, 1, 1}, { -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 1, 1, 1, 1, 1, 1}, { -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 1, 1, 1, 1, 1, 1} }; return sign[x+8][y+8]; } </code></pre> <p>This should be fast as there is no branching that will stall the processor.</p> <p>Using g++ -O3 -S:</p> <pre><code>__Z3fooii: pushl %ebp movl %esp, %ebp movl 8(%ebp), %eax movl 12(%ebp), %edx popl %ebp sall $4, %eax addl %edx, %eax movl _ZZ3fooiiE4sign+544(,%eax,4), %eax ret </code></pre>
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    1. POThree-way conditional in c++ to determine sign equivalance of two numbers
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    1. USMartin York
    1. USMartin York
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    1. COAs usual brute force works well for small domains :)
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      1. USMatthieu M.
    2. COThere is a possibility that computing the value would be faster than using the table due to its frequent reloading to the processor cache. Depends on how the calling code is organized
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      1. USAlsk
    3. CO@Alsk: That may be true but definitely something that would need to be measured to be confirmed. But You also have to remeber that if there is any type of conditional (two in the OP question) then a processor pipeline stall is going to happen and that's not fast either (but faster than fetch from main memory to cache).
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