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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,91 @@ | ||
| //! # Fast power algorithm | ||
|
|
||
| /// Calculate the base ^ power | ||
| /// using the fast powering algorithm | ||
| /// # Arguments | ||
| /// * ` base ` - The base of the exponentiation | ||
| /// * ` power ` - The power of the exponentiation | ||
| /// # Returns | ||
| /// * ` T ` - The result of base ^ power | ||
| /// # Panics | ||
| /// * ` base ` is 0 | ||
| #[feature("deprecated-op-assign-traits")] | ||
| pub fn fast_power< | ||
| T, | ||
| +Div<T>, | ||
| +Rem<T>, | ||
| +Into<u8, T>, | ||
| +Into<T, u256>, | ||
| +TryInto<u256, T>, | ||
| +PartialEq<T>, | ||
| +Copy<T>, | ||
| +Drop<T> | ||
| >( | ||
| base: T, mut power: T | ||
| ) -> T { | ||
| assert!(base != 0_u8.into(), "fast_power: invalid input"); | ||
|
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| let mut base: u256 = base.into(); | ||
| let mut result: u256 = 1; | ||
|
|
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| loop { | ||
| if power % 2_u8.into() != 0_u8.into() { | ||
| result *= base; | ||
| } | ||
| power = power / 2_u8.into(); | ||
| if (power == 0_u8.into()) { | ||
| break; | ||
| } | ||
| base *= base; | ||
| }; | ||
|
|
||
| result.try_into().expect('too large to fit output type') | ||
| } | ||
|
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| /// Calculate the ( base ^ power ) mod modulus | ||
| /// using the fast powering algorithm | ||
| /// # Arguments | ||
| /// * ` base ` - The base of the exponentiation | ||
| /// * ` power ` - The power of the exponentiation | ||
| /// * ` modulus ` - The modulus used in the calculation | ||
| /// # Returns | ||
| /// * ` T ` - The result of ( base ^ power ) mod modulus | ||
| /// # Panics | ||
| /// * ` base ` is 0 | ||
| #[feature("deprecated-op-assign-traits")] | ||
| pub fn fast_power_mod< | ||
| T, | ||
| +Div<T>, | ||
| +Rem<T>, | ||
| +Into<u8, T>, | ||
| +Into<T, u256>, | ||
| +TryInto<u256, T>, | ||
| +PartialEq<T>, | ||
| +Copy<T>, | ||
| +Drop<T> | ||
| >( | ||
| base: T, mut power: T, modulus: T | ||
| ) -> T { | ||
| assert!(base != 0_u8.into(), "fast_power: invalid input"); | ||
|
|
||
| if modulus == 1_u8.into() { | ||
| return 0_u8.into(); | ||
| } | ||
|
|
||
| let mut base: u256 = base.into(); | ||
| let modulus: u256 = modulus.into(); | ||
| let mut result: u256 = 1; | ||
|
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| loop { | ||
| if power % 2_u8.into() != 0_u8.into() { | ||
| result = (result * base) % modulus; | ||
| } | ||
| power = power / 2_u8.into(); | ||
| if (power == 0_u8.into()) { | ||
| break; | ||
| } | ||
| base = (base * base) % modulus; | ||
| }; | ||
|
|
||
| result.try_into().expect('too large to fit output type') | ||
| } |
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