// TODO(gri) can be more efficient if z.prec > 0
	// but small compared to the size of x, or if there
	// are many trailing 0's.
	bits := uint32(x.BitLen())
	if z.prec == 0 {
		z.prec = umax32(bits, 64)
	}
	z.acc = Exact
	z.neg = x.neg
	if len(x.abs) == 0 {
		z.form = zero
		return z
	}
	// x != 0
	z.mant = z.mant.set(x.abs)
	fnorm(z.mant)
	z.setExpAndRound(int64(bits), 0)

	values := []*big.Int{
		// limits
		Uint(maxU64),
		Uint(maxU64 - 1),
		Uint(maxI64 + 1),
		Uint(maxI64),
		Uint(maxI64 - 1),
		Uint(maxU32 + 1),
		Uint(maxU32),
		Uint(maxU32 - 1),
		Uint(maxI32 + 1),
		Uint(maxI32),
		Uint(maxI32 - 1),
		Uint(maxU16 + 1),
		Uint(maxU16),
		Uint(maxU16 - 1),
		Uint(maxI16 + 1),
		Uint(maxI16),
		Uint(maxI16 - 1),
		Uint(maxU8 + 1),
		Uint(maxU8),

		nineteenU + 1, 2*nineteenU - 5, 3*nineteenU + 3, 5*nineteenU + 4, 12345*nineteenU - 2,
		maxU32, maxU32 - 1, maxU32 - 2, maxU32 - 3, maxU32 - 4,
		maxU32 - 5, maxU32 - 6, maxU32 - 7, maxU32 - 8,
		maxU32 - 9, maxU32 - 10, maxU32 - 11, maxU32 - 12,
		maxU32 - 13, maxU32 - 14, maxU32 - 15, maxU32 - 16,
		maxU32 - 17, maxU32 - 18, maxU32 - 19, maxU32 - 20,
		maxU64, maxU64 - 1, maxU64 - 2, maxU64 - 3, maxU64 - 4,

	{0x7f7ffffe, float32(max32 - ulp32), float32(max32 - ulp32 + ulp32/2), "max32 - ulp32 + ulp32/2"},
	{0x7f7fffff, float32(max32), float32(max32 - ulp32 + ulp32/2 + ulp32/two64), "max32 - ulp32 + ulp32/2 + ulp32/two64"},
	{0x7f7fffff, float32(max32), float32(max32 - ulp32/2 + ulp32/two64), "max32 - ulp32/2 + ulp32/two64"},
	{0x7f7fffff, float32(max32), float32(max32), "max32"},

	ulp32 = two128 / two24
	max32 = two128 - ulp32

	ulp64 = two1024 / two53
	max64 = two1024 - ulp64
)

var x = []interface{}{
	float32(max32 + ulp32/2 - 1),             // ok
	float32(max32 + ulp32/2 - two128/two256), // ok
	float32(max32 + ulp32/2),                 // ERROR "constant 3\.40282e\+38 overflows float32|cannot convert.*to type float32"

	float32(-max32 - ulp32/2 + 1),             // ok

	a, b := mix32(uint32(seed), uint32(4^hashkey[0]))
	t := readUnaligned32(p)
	a ^= t
	b ^= t
	a, b = mix32(a, b)
	a, b = mix32(a, b)
	return uintptr(a ^ b)
}

func memhash64Fallback(p unsafe.Pointer, seed uintptr) uintptr {
	a, b := mix32(uint32(seed), uint32(8^hashkey[0]))
	a ^= readUnaligned32(p)
	b ^= readUnaligned32(add(p, 4))
	a, b = mix32(a, b)
	a, b = mix32(a, b)

}

func strmax(x, y string) string {
	if y > x {
		return y
	}
	return x
}

func fmin32(x, y float32) float32 { return fmin(x, y) }
func fmin64(x, y float64) float64 { return fmin(x, y) }
func fmax32(x, y float32) float32 { return fmax(x, y) }
func fmax64(x, y float64) float64 { return fmax(x, y) }

type floaty interface{ ~float32 | ~float64 }

func fmin[F floaty](x, y F) F {
	if y != y || y < x {
		return y

			convInt64:  -0x8000000000000000,
			convUInt64: 0x8000000000000000,
		},
		{
			input:      -0x7ffffffffffffdfe,
			convInt64:  -0x7ffffffffffffc00,
			convUInt64: 0x8000000000000000,
		},
		// umax +- 1
		{
			input:      0xffffffffffffffff,
			convInt64:  -0x8000000000000000,
			convUInt64: 0x8000000000000000,
		},
		{
			input:      0x10000000000000000,
			convInt64:  -0x8000000000000000,

	UBFIZ:     "UBFIZ",
	UBFM:      "UBFM",
	UBFX:      "UBFX",
	UCVTF:     "UCVTF",
	UDIV:      "UDIV",
	UHADD:     "UHADD",
	UHSUB:     "UHSUB",
	UMADDL:    "UMADDL",
	UMAX:      "UMAX",
	UMAXP:     "UMAXP",
	UMAXV:     "UMAXV",
	UMIN:      "UMIN",
	UMINP:     "UMINP",
	UMINV:     "UMINV",
	UMLAL:     "UMLAL",
	UMLAL2:    "UMLAL2",
	UMLSL:     "UMLSL",
	UMLSL2:    "UMLSL2",
	UMNEGL:    "UMNEGL",

	}
	if l.max > l2.max {
		l.max = l2.max
	}
	if l.umax > l2.umax {
		l.umax = l2.umax
	}
	return l
}

var noLimit = limit{math.MinInt64, math.MaxInt64, 0, math.MaxUint64}

// a limitFact is a limit known for a particular value.
type limitFact struct {
	vid   ID
	limit limit
}

// factsTable keeps track of relations between pairs of values.
//