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, 13) :
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
13
1
0
0
1
1
4
13
1
0
0
1
9
2
14
4
7
2
2
2
13
7
2
0
1
11
1
20
6
10
3
3
1
13
10
3
0
1
12
1
10
4
10
4
6
Even
Even
5
2
4
6
↔
1
5
2
10
3
5
3
18
6
9
3
5
3
↔
1
9
3
10
3
2
0
19
6
6
2
1
Even
Even
3
1
6
1
↔
1
3
1
10
3
0
7
1
1
10
3
3
1
0
(10)(4) - (3)(13) = 1