| /*@ Import Lean | |
| import Algorithms.modular_power.lean.spec_lib | |
| open scoped SimpleC | |
| */ | |
| /*@ Extern Coq | |
| (ModularPower : Z -> Z -> Z -> Z -> Prop) | |
| */ | |
| int modular_power(int a, int b, int modulus) | |
| /*@ Require | |
| 0 <= a && a < modulus && | |
| 0 <= b && | |
| 2 <= modulus && modulus <= 46341 && emp | |
| Ensure | |
| 0 <= __return && __return < modulus && | |
| ModularPower(a, b, modulus, __return) && emp | |
| */ | |
| { | |
| int result = 1; | |
| while (b > 0) { | |
| if (b % 2 == 1) { | |
| result = result * a % modulus; | |
| } | |
| a = a * a % modulus; | |
| b /= 2; | |
| } | |
| return result; | |
| } | |