X =
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
Y =
00
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
X ↔ Y
Ext-GCD(4, 9) :
i
GCD
Bezout
AOdd :
AEven :
A
↔
B
ax
ay
bx
by
|A-B|
A↔B
Sx
Sy
ax ←
Sx' ay ←
Sy' A ←
A/2 ax ←
ax + Y ay ←
ay + X ax ←
ax/2 ay ←
ay/2
0
4
9
1
0
0
1
1
4
9
1
0
0
1
5
2
10
4
5
2
2
2
9
5
2
0
1
7
1
14
6
7
3
3
1
9
7
3
0
1
8
1
7
4
7
4
4
16
8
8
4
4
4
↔
1
8
4
7
3
3
2
Even
Even
4
2
5
2
↔
1
4
2
7
3
1
1
Even
Even
2
1
6
1
↔
1
2
1
7
3
0
7
1
1
7
3
2
1
0
(7)(4) - (3)(9) = 1