package math

// Ldexp is the inverse of [Frexp].
// It returns frac × 2**exp.
//
// Special cases are:
//
//	Ldexp(±0, exp) = ±0
//	Ldexp(±Inf, exp) = ±Inf
//	Ldexp(NaN, exp) = NaN
func Ldexp(frac float64, exp int) float64 {
	if haveArchLdexp {
		return archLdexp(frac, exp)
	}
	return ldexp(frac, exp)
}

func ldexp(frac float64, exp int) float64 {
	// special cases
	switch {

	{"64Fixed16", 1.23456e-78, 'e', 16, 64},
	// From testdata/testfp.txt
	{"64Fixed12Hard", math.Ldexp(6965949469487146, -249), 'e', 12, 64},
	{"64Fixed17Hard", math.Ldexp(8887055249355788, 665), 'e', 17, 64},
	{"64Fixed18Hard", math.Ldexp(6994187472632449, 690), 'e', 18, 64},

	// Trigger slow path (see issue #15672).
	// The shortest is: 8.034137530808823e+43
	{"Slowpath64", 8.03413753080882349e+43, 'e', -1, 64},

		return NaN()
	}
	y = Abs(y)

	yfr, yexp := Frexp(y)
	r := x
	if x < 0 {
		r = -x
	}

	for r >= y {
		rfr, rexp := Frexp(r)
		if rfr < yfr {
			rexp = rexp - 1
		}
		r = r - Ldexp(y, rexp-yexp)
	}
	if x < 0 {
		r = -r
	}
	return r

	)

	r := hi - lo
	t := r * r
	c := r - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))))
	y := 1 - ((lo - (r*c)/(2-c)) - hi)
	// TODO(rsc): make sure Ldexp can handle boundary k
	return Ldexp(y, k)

	MULSD   X1, X0
	MOVSD   exprodata<>+16(SB), X1
	ADDSD   X0, X1
	MULSD   X1, X0
	MOVSD   exprodata<>+16(SB), X1
	ADDSD   X0, X1
	MULSD   X1, X0
	ADDSD exprodata<>+8(SB), X0
	// return fr * 2**exponent
ldexp:
	ADDL    $0x3FF, BX // add bias
	JLE     denormal
	CMPL    BX, $0x7FF
	JGE     overflow
lastStep:
	SHLQ    $52, BX
	MOVQ    BX, X1
	MULSD   X1, X0
	MOVSD   X0, ret+8(FP)
	RET
notFinite:

			// on at least one more iteration, ae += xe is a lower bound on ae
			// the lower bound on ae exceeds the size of a float64 exp
			// so the final call to Ldexp will produce under/overflow (0/Inf)
			ae += xe
			break
		}
		if i&1 == 1 {
			a1 *= x1
			ae += xe
		}
		x1 *= x1
		xe <<= 1
		if x1 < .5 {
			x1 += x1
			xe--
		}
	}

	FSUBD	F13, F14
	FMULD	F6, F13, F15
	FDIVD	F14, F15	// F15 = (r*c)/(2-c)
	FSUBD	F15, F5, F15	// lo-(r*c)/(2-c)
	FSUBD	F4, F15, F15	// (lo-(r*c)/(2-c))-hi
	FSUBD	F15, F1, F16	// F16 = y = 1-((lo-(r*c)/(2-c))-hi)
	// inline Ldexp(y, k), benefit:
	// 1, no parameter pass overhead.
	// 2, skip unnecessary checks for Inf/NaN/Zero
	FMOVD	F16, R0
	AND	$FracMask, R0, R2	// fraction
	LSR	$52, R0, R5	// exponent
	ADD	R1, R5		// R1 = int(k)
	CMP	$1, R5

	// arm64:"CSEL\tNE"
	// ppc64x:"ISEL\t[$]2"
	// wasm:"Select"
	return a
}

//go:noinline
func frexp(f float64) (frac float64, exp int) {
	return 1.0, 4
}

//go:noinline
func ldexp(frac float64, exp int) float64 {
	return 1.0
}

// Generate a CMOV with a floating comparison and integer move.
func cmovfloatint2(x, y float64) float64 {
	yfr, yexp := 4.0, 5

	r := x
	for r >= y {

}

func TestLdexp(t *testing.T) {
	for i := 0; i < len(vf); i++ {
		if f := Ldexp(frexp[i].f, frexp[i].i); !veryclose(vf[i], f) {
			t.Errorf("Ldexp(%g, %d) = %g, want %g", frexp[i].f, frexp[i].i, f, vf[i])
		}
	}
	for i := 0; i < len(vffrexpSC); i++ {
		if f := Ldexp(frexpSC[i].f, frexpSC[i].i); !alike(vffrexpSC[i], f) {
			t.Errorf("Ldexp(%g, %d) = %g, want %g", frexpSC[i].f, frexpSC[i].i, f, vffrexpSC[i])
		}
	}

					f, _ := r.Float32()

					if !checkIsBestApprox32(t, f, r) {
						// Append context information.
						t.Errorf("(input was mantissa %#x, exp %d; f = %g (%b); f ~ %g; r = %v)",
							b, exp, f, f, math.Ldexp(float64(b), exp), r)
					}

					checkNonLossyRoundtrip32(t, f)
				}
			}
		}
	}
}

func TestFloat64Distribution(t *testing.T) {
	// Generate a distribution of (sign, mantissa, exp) values