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(2, 15) :
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
2
15
1
0
0
1
1
2
15
1
0
0
1
13
1
16
2
8
1
2
1
15
8
1
0
1
14
1
8
2
8
2
7
Even
Even
4
1
3
7
↔
1
4
1
8
1
6
0
12
2
12
2
3
Even
Even
6
1
4
3
↔
1
6
1
8
1
2
0
14
2
14
2
1
Even
Even
7
1
5
1
↔
1
7
1
8
1
0
6
1
↔
1
7
1
8
1
0
7
1
1
8
1
7
1
0
(8)(2) - (1)(15) = 1