*/

// This implementation is based on the rational approximation
// of percentage points of normal distribution available from
// https://www.jstor.org/stable/2347330.

const (
	// Coefficients for approximation to erf in |x| <= 0.85
	a0 = 1.1975323115670912564578e0
	a1 = 4.7072688112383978012285e1
	a2 = 6.9706266534389598238465e2
	a3 = 4.8548868893843886794648e3
	a4 = 1.6235862515167575384252e4
	a5 = 2.3782041382114385731252e4

// Outlines non-approximate GELU into a stablehlo composite.
//
//    -> mul 1/sqrt(2) -> erf -> add 1 ->
// in                                    mul
//    ---------> mul 0.5 --------------->
//
// This pattern assumes all binary ewise ops with one constant argument
// have that constant argument as the second operand. It works by
// identifying `erf` ops and validate the structure around them.
class OutlineGELU : public RewritePattern {