github.com/afumu/libc@v0.0.6/musl/src/math/x86_64/fabs.c (about)

     1  #include <math.h>
     2  
     3  double fabs(double x)
     4  {
     5  	double t;
     6  	__asm__ ("pcmpeqd %0, %0" : "=x"(t));          // t = ~0
     7  	__asm__ ("psrlq   $1, %0" : "+x"(t));          // t >>= 1
     8  	__asm__ ("andps   %1, %0" : "+x"(x) : "x"(t)); // x &= t
     9  	return x;
    10  }