--- /dev/null
+#if !defined(_egcd_H)
+# define _egcd_H (1)
+
+/*Computes the coefficients of the smallest positive linear combination of two
+ integers _a and _b.
+ These are a solution (u,v) to the equation _a*u+_b*v==gcd(_a,_b).
+ _a: The first integer of which to compute the extended gcd.
+ _b: The second integer of which to compute the extended gcd.
+ _u: Returns the coefficient of _a in the smallest positive linear
+ combination.
+ _v: Returns the coefficient _of b in the smallest positive linear
+ combination.
+ Return: The non-negative gcd of _a and _b.
+ If _a and _b are both 0, then 0 is returned, though in reality the
+ gcd is undefined, as any integer, no matter how large, will divide 0
+ evenly.
+ _a*u+_b*v will not be positive in this case.
+ Note that the solution (u,v) of _a*u+_b*v==gcd(_a,_b) returned is not
+ unique.
+ (u+(_b/gcd(_a,_b))*k,v-(_a/gcd(_a,_b))*k) is also a solution for all
+ k.
+ The coefficients (u,v) might not be positive.*/
+int egcd(int _a,int _b,int *_u,int *_v);
+
+#endif