Exemple #1
0
func SqrtShiftU64(x uint64) uint64 {
	// The highest set bit of the square root of x is equal to
	// log2(x)/2, and always fits in a 32bit word. Using uint
	// instead of uint64 guarantees native word width, which
	// is 7/4 faster on my 32bit netbook.
	r := uint(1 << (u64.Log2(x) >> 1))
	s := r >> 1
	t := r + s
	for s > 0 {
		if uint64(t)*uint64(t) <= x {
			r = t
		}
		s >>= 1
		t = r + s
	}
	return uint64(r)
}
Exemple #2
0
func TestLog2(t *testing.T) {
	t.Log("Testing Log2\n")
	iMax := uint(1)
	if iMax<<32 == 0 {
		iMax = 31
	} else {
		iMax = 63
	}
	for i := uint(0); i < iMax; i++ {
		for j := uint(0); j < i; j++ {
			k := int((1 << i) + (1 << j))
			if intgr.Log2(k) != int(i) {
				t.Logf("intgr.Log2(%v) == %v\n", k, intgr.Log2(k))
				t.FailNow()
			}
		}
	}
	if intgr.Log2(-1) != -1 {
		t.Logf("intgr.Log2(-1) == %v\n", intgr.Log2(-1))
		t.FailNow()
	}

	for i := uint(0); i < iMax; i++ {
		for j := uint(0); j < i; j++ {
			k := uint((1 << i) + (1 << j))
			if uintgr.Log2(k) != i {
				t.Logf("intgr.Log2(%v) == %v\n", k, uintgr.Log2(k))
				t.Fail()
			}
		}
	}

	for i := uint32(0); i < uint32(31); i++ {
		for j := uint32(0); j < i; j++ {
			k := int32((1 << i) + (1 << j))
			if i32.Log2(k) != int32(i) {
				t.Logf("i32.Log2(%v) == %v\n", k, i32.Log2(k))
				t.FailNow()
			}
		}
	}
	if i32.Log2(-1) != int32(-1) {
		t.Logf("i32.Log2(-1) == %v\n", i32.Log2(-1))
		t.FailNow()
	}

	for i := uint32(0); i < uint32(31); i++ {
		for j := uint32(0); j < i; j++ {
			k := uint32((1 << i) + (1 << j))
			if u32.Log2(k) != i {
				t.Logf("u32.Log2(%v) == %v\n", k, u32.Log2(k))
				t.FailNow()
			}
		}
	}

	for i := uint64(0); i < uint64(63); i++ {
		for j := uint64(0); j < i; j++ {
			k := int64((1 << i) + (1 << j))
			if i64.Log2(k) != int64(i) {
				t.Logf("i64.Log2(%v) == %v\n", k, i64.Log2(k))
				t.FailNow()
			}
		}
	}
	if i64.Log2(-1) != int64(-1) {
		t.Logf("i64.Log2(-1) == %v\n", i64.Log2(-1))
		t.FailNow()
	}

	for i := uint64(0); i < uint64(63); i++ {
		for j := uint64(0); j < i; j++ {
			k := uint64((1 << i) + (1 << j))
			if u64.Log2(k) != i {
				t.Logf("u64.Log2(%v) == %v\n", k, u64.Log2(k))
				t.FailNow()
			}
		}
	}
}