diff --git a/bigint/src/bigint.rs b/bigint/src/bigint.rs index 32a4441..0379591 100644 --- a/bigint/src/bigint.rs +++ b/bigint/src/bigint.rs @@ -1,5 +1,5 @@ use std::default::Default; -use std::ops::{Add, Div, Mul, Neg, Rem, Shl, Shr, Sub}; +use std::ops::{Add, Div, Mul, Neg, Rem, Shl, Shr, Sub, Not}; use std::str::{self, FromStr}; use std::fmt; use std::cmp::Ordering::{self, Less, Greater, Equal}; @@ -16,8 +16,8 @@ use serde; use rand::Rng; use integer::Integer; -use traits::{ToPrimitive, FromPrimitive, Num, CheckedAdd, CheckedSub, CheckedMul, - CheckedDiv, Signed, Zero, One}; +use traits::{ToPrimitive, FromPrimitive, Num, WrappingAdd, CheckedAdd, CheckedSub, + CheckedMul, CheckedDiv, Signed, Zero, One}; use self::Sign::{Minus, NoSign, Plus}; @@ -926,6 +926,56 @@ impl BigInt { BigInt::from_biguint(sign, BigUint::new(digits)) } + /// Creates and initializes a `BigInt` from an array of bytes in two's complement. + /// + /// The digits are in little-endian base 2^8. + #[inline] + pub fn from_twos_complement_bytes_le(mut digits: Vec) -> BigInt { + let sign = if digits.iter().all(Zero::is_zero) { + Sign::NoSign + } else { + digits.iter().rev().next() + .map(|v| if *v > 127 { + Sign::Minus + } else { + Sign::Plus + }) + // we have at least one non-zero digit + .unwrap() + }; + + if sign == Sign::Minus { + // two's-complement the content to retrieve the magnitude + twos_complement_le(&mut digits); + } + BigInt::from_biguint(sign, BigUint::from_bytes_le(&*digits)) + } + + /// Creates and initializes a `BigInt` from an array of bytes in two's complement. + /// + /// The digits are in big-endian base 2^8. + #[inline] + pub fn from_twos_complement_bytes_be(mut digits: Vec) -> BigInt { + let sign = if digits.iter().all(Zero::is_zero) { + Sign::NoSign + } else { + digits.iter().next() + .map(|v| if *v > 127 { + Sign::Minus + } else { + Sign::Plus + }) + // we have at least one non-zero digit + .unwrap() + }; + + if sign == Sign::Minus { + // two's-complement the content to retrieve the magnitude + twos_complement_be(&mut digits); + } + BigInt::from_biguint(sign, BigUint::from_bytes_be(&*digits)) + } + /// Creates and initializes a `BigInt`. /// /// The digits are in little-endian base 2^32. @@ -994,6 +1044,23 @@ impl BigInt { pub fn to_bytes_le(&self) -> (Sign, Vec) { (self.sign, self.data.to_bytes_le()) } + + /// Returns the two's complement byte representation of the `BigInt` in little-endian byte order. + /// + /// # Examples + /// + /// ``` + /// use num_bigint::ToBigInt; + /// + /// let i = -1125.to_bigint().unwrap(); + /// assert_eq!(i.to_twos_complement_bytes_le(), vec![155, 251]); + /// ``` + #[inline] + pub fn to_twos_complement_bytes_le(&self) -> Vec { + let mut bytes = self.data.to_bytes_le(); + twos_complement_le(&mut bytes); + bytes + } /// Returns the sign and the byte representation of the `BigInt` in big-endian byte order. /// @@ -1010,6 +1077,23 @@ impl BigInt { (self.sign, self.data.to_bytes_be()) } + /// Returns the two's complement byte representation of the `BigInt` in big-endian byte order. + /// + /// # Examples + /// + /// ``` + /// use num_bigint::ToBigInt; + /// + /// let i = -1125.to_bigint().unwrap(); + /// assert_eq!(i.to_twos_complement_bytes_be(), vec![251, 155]); + /// ``` + #[inline] + pub fn to_twos_complement_bytes_be(&self) -> Vec { + let mut bytes = self.data.to_bytes_be(); + twos_complement_be(&mut bytes); + bytes + } + /// Returns the integer formatted as a string in the given radix. /// `radix` must be in the range `[2, 36]`. /// @@ -1105,3 +1189,36 @@ impl BigInt { return Some(self.div(v)); } } + +/// Perform in-place two's complement of the given digit range, +/// in little-endian byte order. +#[inline] +fn twos_complement_le(digits: &mut [T]) + where T: Clone + Not + WrappingAdd + Zero + One +{ + let mut carry = true; + for d in digits { + *d = d.clone().not(); + if carry { + *d = d.wrapping_add(&T::one()); + carry = d.is_zero(); + } + } +} + +/// Perform in-place two's complement of the given digit range +/// in big-endian byte order. +#[inline] +fn twos_complement_be(digits: &mut [T]) + where T: Clone + Not + WrappingAdd + Zero + One +{ + let mut carry = true; + for d in digits.iter_mut().rev() { + *d = d.clone().not(); + if carry { + *d = d.wrapping_add(&T::one()); + carry = d.is_zero(); + } + } +} + diff --git a/bigint/src/tests/bigint.rs b/bigint/src/tests/bigint.rs index bb8899e..ead3452 100644 --- a/bigint/src/tests/bigint.rs +++ b/bigint/src/tests/bigint.rs @@ -106,6 +106,43 @@ fn test_to_bytes_le() { assert_eq!(b.to_bytes_le(), (Plus, vec![0, 2, 0, 0, 0, 0, 0, 0, 1])); } +#[test] +fn test_from_twos_complement_bytes_le() { + fn check(s: Vec, result: &str) { + assert_eq!(BigInt::from_twos_complement_bytes_le(s), + BigInt::parse_bytes(result.as_bytes(), 10).unwrap()); + } + + check(vec![], "0"); + check(vec![0], "0"); + check(vec![0; 10], "0"); + check(vec![255, 127], "32767"); + check(vec![255], "-1"); + check(vec![0, 0, 0, 1], "16777216"); + check(vec![156], "-100"); + check(vec![0, 0, 128], "-8388608"); + check(vec![255; 10], "-1"); +} + +#[test] +fn test_from_twos_complement_bytes_be() { + fn check(s: Vec, result: &str) { + assert_eq!(BigInt::from_twos_complement_bytes_be(s), + BigInt::parse_bytes(result.as_bytes(), 10).unwrap()); + } + + check(vec![], "0"); + check(vec![0], "0"); + check(vec![0; 10], "0"); + check(vec![127, 255], "32767"); + check(vec![255], "-1"); + check(vec![1, 0, 0, 0], "16777216"); + check(vec![156], "-100"); + check(vec![128, 0, 0], "-8388608"); + check(vec![255; 10], "-1"); +} + + #[test] fn test_cmp() { let vs: [&[BigDigit]; 4] = [&[2 as BigDigit], &[1, 1], &[2, 1], &[1, 1, 1]];