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POHow to get `gcc` to generate `bts` instruction for x86-64 from standard C?
 

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  1. POHow to get `gcc` to generate `bts` instruction for x86-64 from standard C?
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    <p>Inspired by a <a href="https://stackoverflow.com/questions/2039592/effectiveness-of-gcc-optmization-on-bit-operations">recent question</a>, I'd like to know if anyone knows how to get <code>gcc</code> to generate the x86-64 <code>bts</code> instruction (bit test and set) on the Linux x86-64 platforms, <em>without</em> resorting to inline assembly or to nonstandard compiler intrinsics.</p> <p>Related questions:</p> <ul> <li><p><a href="https://stackoverflow.com/questions/2039592/effectiveness-of-gcc-optmization-on-bit-operations">Why doesn't gcc do this for a simple <code>|=</code> operation were the right-hand side has exactly 1 bit set?</a></p></li> <li><p><a href="https://stackoverflow.com/questions/1983303/using-bts-assembly-instruction-with-gcc-compiler">How to get <code>bts</code> using compiler intrinsics or the <code>asm</code> directive</a></p></li> </ul> <p>Portability is more important to me than <code>bts</code>, so I won't use and <code>asm</code> directive, and if there's another solution, I prefer not to use compiler instrinsics.</p> <p><strong>EDIT</strong>: The C source language does not support atomic operations, so I'm not particularly interested in getting <em>atomic</em> test-and-set (even though that's the original reason for test-and-set to exist in the first place). If I want something atomic I know I have no chance of doing it with standard C source: it has to be an intrinsic, a library function, or inline assembly. (I have implemented atomic operations in compilers that support multiple threads.)</p>
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    1. USNorman Ramsey
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      1. POHow to get `gcc` to generate `bts` instruction for x86-64 from standard C?
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      1. POHow to get `gcc` to generate `bts` instruction for x86-64 from standard C?
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    1. COHmm, good question. I see `vtst_*` for vector bit-test on ARM+NEON, but nothing more general...
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      1. POHow to get `gcc` to generate `bts` instruction for x86-64 from standard C?
      1. USephemient
    2. COIf bts is really faster, send a bug report. I am sure gcc programmers are already aware of bts' existance. After all, a compiler isn't supposed to map 1:1.
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      1. POHow to get `gcc` to generate `bts` instruction for x86-64 from standard C?
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    3. COBetter still, send a patch to use bts together with testcases that can be profiled to prove that the optimization is worthwhile.
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      1. POHow to get `gcc` to generate `bts` instruction for x86-64 from standard C?
      1. USStephen C
 

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