llvm-project/libclc/generic/lib/math/acos.inc

/*
 * There are multiple formulas for calculating arccosine of x:
 * 1) acos(x) = (1/2*pi) + i * ln(i*x + sqrt(1-x^2)) (notice the 'i'...)
 * 2) acos(x) = pi/2 + asin(-x) (asin isn't implemented yet)
 * 3) acos(x) = pi/2 - asin(x) (ditto)
 * 4) acos(x) = 2*atan2(sqrt(1-x), sqrt(1+x))
 * 5) acos(x) = pi/2 - atan2(x, ( sqrt(1-x^2) ) )
 *
 * Options 1-3 are not currently usable, #5 generates more concise radeonsi
 * bitcode and assembly than #4 (134 vs 132 instructions on radeonsi), but
 * precision of #4 may be better.
 */

#if __CLC_FPSIZE == 32
#define __CLC_CONST(x) x ## f
#else
#define __CLC_CONST(x) x
#endif

_CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE acos(__CLC_GENTYPE x) {
  return (
    (__CLC_GENTYPE) __CLC_CONST(2.0) * atan2(
      sqrt((__CLC_GENTYPE) __CLC_CONST(1.0) - x),
      sqrt((__CLC_GENTYPE) __CLC_CONST(1.0) + x)
    )
  );
}

#undef __CLC_CONST