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, 7) :
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
7
1
0
0
1
1
4
7
1
0
0
1
3
2
8
4
4
2
2
2
7
4
2
0
1
5
1
Even
Even
2
1
3
1
7
2
1
0
1
6
1
2
2
2
2
3
Even
Even
1
1
4
3
↔
1
1
1
2
1
2
0
3
2
3
2
1
10
6
5
3
5
1
↔
1
5
3
2
1
0
6
1
↔
1
5
3
2
1
0
7
1
1
2
1
5
3
0
(2)(4) - (1)(7) = 1