12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485 |
- #include "os.h"
- #include <mp.h>
- // extended euclid
- //
- // For a and b it solves, d = gcd(a,b) and finds x and y s.t.
- // ax + by = d
- //
- // Handbook of Applied Cryptography, Menezes et al, 1997, pg 67
- void
- mpeuclid(mpint *a, mpint *b, mpint *d, mpint *x, mpint *y)
- {
- mpint *tmp, *x0, *x1, *x2, *y0, *y1, *y2, *q, *r;
- if(a->sign<0 || b->sign<0)
- sysfatal("mpeuclid: negative arg");
- if(mpcmp(a, b) < 0){
- tmp = a;
- a = b;
- b = tmp;
- tmp = x;
- x = y;
- y = tmp;
- }
- if(b->top == 0){
- mpassign(a, d);
- mpassign(mpone, x);
- mpassign(mpzero, y);
- return;
- }
- a = mpcopy(a);
- b = mpcopy(b);
- x0 = mpnew(0);
- x1 = mpcopy(mpzero);
- x2 = mpcopy(mpone);
- y0 = mpnew(0);
- y1 = mpcopy(mpone);
- y2 = mpcopy(mpzero);
- q = mpnew(0);
- r = mpnew(0);
- while(b->top != 0 && b->sign > 0){
- // q = a/b
- // r = a mod b
- mpdiv(a, b, q, r);
- // x0 = x2 - qx1
- mpmul(q, x1, x0);
- mpsub(x2, x0, x0);
- // y0 = y2 - qy1
- mpmul(q, y1, y0);
- mpsub(y2, y0, y0);
- // rotate values
- tmp = a;
- a = b;
- b = r;
- r = tmp;
- tmp = x2;
- x2 = x1;
- x1 = x0;
- x0 = tmp;
- tmp = y2;
- y2 = y1;
- y1 = y0;
- y0 = tmp;
- }
- mpassign(a, d);
- mpassign(x2, x);
- mpassign(y2, y);
- mpfree(x0);
- mpfree(x1);
- mpfree(x2);
- mpfree(y0);
- mpfree(y1);
- mpfree(y2);
- mpfree(q);
- mpfree(r);
- mpfree(a);
- mpfree(b);
- }
|