I find myself typing

double foo=1.0/sqrt(...);

a lot, and I've heard that modern processors have built-in inverse square root opcodes.

Is there a C or C++ standard library inverse square root function that

  1. uses double precision floating point?
  2. is as accurate as 1.0/sqrt(...)?
  3. is just as fast or faster than the result of 1.0/sqrt(...)?
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