Struct ethnum::U256

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#[repr(transparent)]
pub struct U256(pub [u128; 2]);

Expand description

A 256-bit unsigned integer type.

Tuple Fields§

§0: [u128; 2]

Implementations§

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impl U256

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pub const MIN: Self = _

The smallest value that can be represented by this integer type.

pub const MAX: Self = _

The largest value that can be represented by this integer type.

pub const BITS: u32 = 256u32

The size of this integer type in bits.

pub fn from_str_radix(src: &str, radix: u32) -> Result<Self, ParseIntError>

Converts a string slice in a given base to an integer.

The string is expected to be an optional + sign followed by digits. Leading and trailing whitespace represent an error. Digits are a subset of these characters, depending on radix:

0-9
a-z
A-Z

Panics

This function panics if radix is not in the range from 2 to 36.

pub const fn count_ones(self) -> u32

Returns the number of ones in the binary representation of self.

pub const fn count_zeros(self) -> u32

Returns the number of zeros in the binary representation of self.

pub fn leading_zeros(self) -> u32

Returns the number of leading zeros in the binary representation of self.

pub fn trailing_zeros(self) -> u32

Returns the number of trailing zeros in the binary representation of self.

pub fn leading_ones(self) -> u32

Returns the number of leading ones in the binary representation of self.

pub fn trailing_ones(self) -> u32

Returns the number of trailing ones in the binary representation of self.

pub fn rotate_left(self, n: u32) -> Self

Shifts the bits to the left by a specified amount, n, wrapping the truncated bits to the end of the resulting integer.

Please note this isn’t the same operation as the << shifting operator!

pub fn rotate_right(self, n: u32) -> Self

Shifts the bits to the right by a specified amount, n, wrapping the truncated bits to the beginning of the resulting integer.

Please note this isn’t the same operation as the >> shifting operator!

pub const fn swap_bytes(self) -> Self

Reverses the byte order of the integer.

pub const fn reverse_bits(self) -> Self

Reverses the bit pattern of the integer.

pub const fn from_be(x: Self) -> Self

Converts an integer from big endian to the target’s endianness.

On big endian this is a no-op. On little endian the bytes are swapped.

pub const fn from_le(x: Self) -> Self

Converts an integer from little endian to the target’s endianness.

On little endian this is a no-op. On big endian the bytes are swapped.

pub const fn to_be(self) -> Self

Converts self to big endian from the target’s endianness.

On big endian this is a no-op. On little endian the bytes are swapped.

pub const fn to_le(self) -> Self

Converts self to little endian from the target’s endianness.

On little endian this is a no-op. On big endian the bytes are swapped.

pub fn checked_add(self, rhs: Self) -> Option<Self>

Checked integer addition. Computes self + rhs, returning None if overflow occurred.

pub fn checked_add_signed(self, rhs: I256) -> Option<Self>

Checked addition with a signed integer. Computes self + rhs, returning None if overflow occurred.

pub fn checked_sub(self, rhs: Self) -> Option<Self>

Checked integer subtraction. Computes self - rhs, returning None if overflow occurred.

pub fn checked_mul(self, rhs: Self) -> Option<Self>

Checked integer multiplication. Computes self * rhs, returning None if overflow occurred.

pub fn checked_div(self, rhs: Self) -> Option<Self>

Checked integer division. Computes self / rhs, returning None if rhs == 0.

pub fn checked_div_euclid(self, rhs: Self) -> Option<Self>

Checked Euclidean division. Computes self.div_euclid(rhs), returning None if rhs == 0.

pub fn checked_rem(self, rhs: Self) -> Option<Self>

Checked integer remainder. Computes self % rhs, returning None if rhs == 0.

pub fn checked_rem_euclid(self, rhs: Self) -> Option<Self>

Checked Euclidean modulo. Computes self.rem_euclid(rhs), returning None if rhs == 0.

pub fn checked_neg(self) -> Option<Self>

Checked negation. Computes -self, returning None unless self == 0.

Note that negating any positive integer will overflow.

pub fn checked_shl(self, rhs: u32) -> Option<Self>

Checked shift left. Computes self << rhs, returning None if rhs is larger than or equal to the number of bits in self.

pub fn checked_shr(self, rhs: u32) -> Option<Self>

Checked shift right. Computes self >> rhs, returning None if rhs is larger than or equal to the number of bits in self.

pub fn checked_pow(self, exp: u32) -> Option<Self>

Checked exponentiation. Computes self.pow(exp), returning None if overflow occurred.

pub fn saturating_add(self, rhs: Self) -> Self

Saturating integer addition. Computes self + rhs, saturating at the numeric bounds instead of overflowing.

pub fn saturating_add_signed(self, rhs: I256) -> Self

Saturating addition with a signed integer. Computes self + rhs, saturating at the numeric bounds instead of overflowing.

pub fn saturating_sub(self, rhs: Self) -> Self

Saturating integer subtraction. Computes self - rhs, saturating at the numeric bounds instead of overflowing.

pub fn saturating_mul(self, rhs: Self) -> Self

Saturating integer multiplication. Computes self * rhs, saturating at the numeric bounds instead of overflowing.

pub fn saturating_div(self, rhs: Self) -> Self

Saturating integer division. Computes self / rhs, saturating at the numeric bounds instead of overflowing.

pub fn saturating_pow(self, exp: u32) -> Self

Saturating integer exponentiation. Computes self.pow(exp), saturating at the numeric bounds instead of overflowing.

pub fn wrapping_add(self, rhs: Self) -> Self

Wrapping (modular) addition. Computes self + rhs, wrapping around at the boundary of the type.

pub fn wrapping_add_signed(self, rhs: I256) -> Self

Wrapping (modular) addition with a signed integer. Computes self + rhs, wrapping around at the boundary of the type.

pub fn wrapping_sub(self, rhs: Self) -> Self

Wrapping (modular) subtraction. Computes self - rhs, wrapping around at the boundary of the type.

pub fn wrapping_mul(self, rhs: Self) -> Self

Wrapping (modular) multiplication. Computes self * rhs, wrapping around at the boundary of the type.

pub fn wrapping_div(self, rhs: Self) -> Self

Wrapping (modular) division. Computes self / rhs. Wrapped division on unsigned types is just normal division. There’s no way wrapping could ever happen. This function exists, so that all operations are accounted for in the wrapping operations.

Examples

Basic usage:

assert_eq!(U256::new(100).wrapping_div(U256::new(10)), U256::new(10));

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pub fn wrapping_div_euclid(self, rhs: Self) -> Self

Wrapping Euclidean division. Computes self.div_euclid(rhs). Wrapped division on unsigned types is just normal division. There’s no way wrapping could ever happen. This function exists, so that all operations are accounted for in the wrapping operations. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.wrapping_div(rhs).

Examples

Basic usage:

assert_eq!(U256::new(100).wrapping_div_euclid(U256::new(10)), U256::new(10));

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pub fn wrapping_rem(self, rhs: Self) -> Self

Wrapping (modular) remainder. Computes self % rhs. Wrapped remainder calculation on unsigned types is just the regular remainder calculation. There’s no way wrapping could ever happen. This function exists, so that all operations are accounted for in the wrapping operations.

Examples

Basic usage:

assert_eq!(U256::new(100).wrapping_rem(U256::new(10)), U256::new(0));

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pub fn wrapping_rem_euclid(self, rhs: Self) -> Self

Wrapping Euclidean modulo. Computes self.rem_euclid(rhs). Wrapped modulo calculation on unsigned types is just the regular remainder calculation. There’s no way wrapping could ever happen. This function exists, so that all operations are accounted for in the wrapping operations. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.wrapping_rem(rhs).

Examples

Basic usage:

assert_eq!(U256::new(100).wrapping_rem_euclid(U256::new(10)), U256::new(0));

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pub fn wrapping_neg(self) -> Self

Wrapping (modular) negation. Computes -self, wrapping around at the boundary of the type.

Since unsigned types do not have negative equivalents all applications of this function will wrap (except for -0). For values smaller than the corresponding signed type’s maximum the result is the same as casting the corresponding signed value. Any larger values are equivalent to MAX + 1 - (val - MAX - 1) where MAX is the corresponding signed type’s maximum.

Examples

Basic usage:

Please note that this example is shared between integer types. Which explains why i8 is used here.

assert_eq!(U256::new(100).wrapping_neg(), (-100i128).as_u256());
assert_eq!(
    U256::from_words(i128::MIN as _, 0).wrapping_neg(),
    U256::from_words(i128::MIN as _, 0),
);

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pub fn wrapping_shl(self, rhs: u32) -> Self

Panic-free bitwise shift-left; yields self << mask(rhs), where mask removes any high-order bits of rhs that would cause the shift to exceed the bitwidth of the type.

Note that this is not the same as a rotate-left; the RHS of a wrapping shift-left is restricted to the range of the type, rather than the bits shifted out of the LHS being returned to the other end. The primitive integer types all implement a rotate_left function, which maybe what you want instead.

Examples

Basic usage:

assert_eq!(U256::new(1).wrapping_shl(7), U256::new(128));
assert_eq!(U256::new(1).wrapping_shl(128), U256::from_words(1, 0));
assert_eq!(U256::new(1).wrapping_shl(256), U256::new(1));

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pub fn wrapping_shr(self, rhs: u32) -> Self

Panic-free bitwise shift-right; yields self >> mask(rhs), where mask removes any high-order bits of rhs that would cause the shift to exceed the bitwidth of the type.

Note that this is not the same as a rotate-right; the RHS of a wrapping shift-right is restricted to the range of the type, rather than the bits shifted out of the LHS being returned to the other end. The primitive integer types all implement a rotate_right function, which may be what you want instead.

Examples

Basic usage:

assert_eq!(U256::new(128).wrapping_shr(7), U256::new(1));
assert_eq!(U256::from_words(128, 0).wrapping_shr(128), U256::new(128));
assert_eq!(U256::new(128).wrapping_shr(256), U256::new(128));

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pub fn wrapping_pow(self, exp: u32) -> Self

Wrapping (modular) exponentiation. Computes self.pow(exp), wrapping around at the boundary of the type.

Examples

Basic usage:

assert_eq!(U256::new(3).wrapping_pow(5), U256::new(243));
assert_eq!(
    U256::new(1337).wrapping_pow(42),
    U256::from_words(
        45367329835866155830012179193722278514,
        159264946433345088039815329994094210673,
    ),
);

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pub fn overflowing_add(self, rhs: Self) -> (Self, bool)

Calculates self + rhs

Returns a tuple of the addition along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

Basic usage

assert_eq!(U256::new(5).overflowing_add(U256::new(2)), (U256::new(7), false));
assert_eq!(U256::MAX.overflowing_add(U256::new(1)), (U256::new(0), true));

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pub fn overflowing_add_signed(self, rhs: I256) -> (Self, bool)

Calculates self + rhs with a signed rhs

Returns a tuple of the addition along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

Basic usage:

assert_eq!(U256::new(1).overflowing_add_signed(I256::new(2)), (U256::new(3), false));
assert_eq!(U256::new(1).overflowing_add_signed(I256::new(-2)), (U256::MAX, true));
assert_eq!((U256::MAX - 2).overflowing_add_signed(I256::new(4)), (U256::new(1), true));

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pub fn overflowing_sub(self, rhs: Self) -> (Self, bool)

Calculates self - rhs

Returns a tuple of the subtraction along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

Basic usage

assert_eq!(U256::new(5).overflowing_sub(U256::new(2)), (U256::new(3), false));
assert_eq!(U256::new(0).overflowing_sub(U256::new(1)), (U256::MAX, true));

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pub fn abs_diff(self, other: Self) -> Self

Computes the absolute difference between self and other.

Examples

Basic usage:

assert_eq!(U256::new(100).abs_diff(U256::new(80)), 20);
assert_eq!(U256::new(100).abs_diff(U256::new(110)), 10);

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pub fn overflowing_mul(self, rhs: Self) -> (Self, bool)

Calculates the multiplication of self and rhs.

Returns a tuple of the multiplication along with a boolean indicating whether an arithmetic overflow would occur. If an overflow would have occurred then the wrapped value is returned.

Examples

Basic usage:

Please note that this example is shared between integer types. Which explains why u32 is used here.

assert_eq!(U256::new(5).overflowing_mul(U256::new(2)), (U256::new(10), false));
assert_eq!(
    U256::MAX.overflowing_mul(U256::new(2)),
    (U256::MAX - 1, true),
);

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pub fn overflowing_div(self, rhs: Self) -> (Self, bool)

Calculates the divisor when self is divided by rhs.

Returns a tuple of the divisor along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false.

Panics

This function will panic if rhs is 0.

Examples

Basic usage

assert_eq!(U256::new(5).overflowing_div(U256::new(2)), (U256::new(2), false));

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pub fn overflowing_div_euclid(self, rhs: Self) -> (Self, bool)

Calculates the quotient of Euclidean division self.div_euclid(rhs).

Returns a tuple of the divisor along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false. Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self.overflowing_div(rhs).

Panics

This function will panic if rhs is 0.

Examples

Basic usage

assert_eq!(U256::new(5).overflowing_div_euclid(U256::new(2)), (U256::new(2), false));

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pub fn overflowing_rem(self, rhs: Self) -> (Self, bool)

Calculates the remainder when self is divided by rhs.

Returns a tuple of the remainder after dividing along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false.

Panics

This function will panic if rhs is 0.

Examples

Basic usage

assert_eq!(U256::new(5).overflowing_rem(U256::new(2)), (U256::new(1), false));

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pub fn overflowing_rem_euclid(self, rhs: Self) -> (Self, bool)

Calculates the remainder self.rem_euclid(rhs) as if by Euclidean division.

Returns a tuple of the modulo after dividing along with a boolean indicating whether an arithmetic overflow would occur. Note that for unsigned integers overflow never occurs, so the second value is always false. Since, for the positive integers, all common definitions of division are equal, this operation is exactly equal to self.overflowing_rem(rhs).

Panics

This function will panic if rhs is 0.

Examples

Basic usage

assert_eq!(U256::new(5).overflowing_rem_euclid(U256::new(2)), (U256::new(1), false));

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pub fn overflowing_neg(self) -> (Self, bool)

Negates self in an overflowing fashion.

Returns !self + 1 using wrapping operations to return the value that represents the negation of this unsigned value. Note that for positive unsigned values overflow always occurs, but negating 0 does not overflow.

Examples

Basic usage

assert_eq!(U256::new(0).overflowing_neg(), (U256::new(0), false));
assert_eq!(U256::new(2).overflowing_neg(), ((-2i32).as_u256(), true));

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pub fn overflowing_shl(self, rhs: u32) -> (Self, bool)

Shifts self left by rhs bits.

Returns a tuple of the shifted version of self along with a boolean indicating whether the shift value was larger than or equal to the number of bits. If the shift value is too large, then value is masked (N-1) where N is the number of bits, and this value is then used to perform the shift.

Examples

Basic usage

assert_eq!(U256::new(0x1).overflowing_shl(4), (U256::new(0x10), false));
assert_eq!(U256::new(0x1).overflowing_shl(260), (U256::new(0x10), true));

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pub fn overflowing_shr(self, rhs: u32) -> (Self, bool)

Shifts self right by rhs bits.

Returns a tuple of the shifted version of self along with a boolean indicating whether the shift value was larger than or equal to the number of bits. If the shift value is too large, then value is masked (N-1) where N is the number of bits, and this value is then used to perform the shift.

Examples

Basic usage

assert_eq!(U256::new(0x10).overflowing_shr(4), (U256::new(0x1), false));
assert_eq!(U256::new(0x10).overflowing_shr(260), (U256::new(0x1), true));

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pub fn overflowing_pow(self, exp: u32) -> (Self, bool)

Raises self to the power of exp, using exponentiation by squaring.

Returns a tuple of the exponentiation along with a bool indicating whether an overflow happened.

Examples

Basic usage:

assert_eq!(U256::new(3).overflowing_pow(5), (U256::new(243), false));
assert_eq!(
    U256::new(1337).overflowing_pow(42),
    (
        U256::from_words(
            45367329835866155830012179193722278514,
            159264946433345088039815329994094210673,
        ),
        true,
    )
);

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pub fn pow(self, exp: u32) -> Self

Raises self to the power of exp, using exponentiation by squaring.

Examples

Basic usage:

assert_eq!(U256::new(2).pow(5), U256::new(32));

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pub fn div_euclid(self, rhs: Self) -> Self

Performs Euclidean division.

Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self / rhs.

Panics

This function will panic if rhs is 0.

Examples

Basic usage:

assert_eq!(U256::new(7).div_euclid(U256::new(4)), U256::new(1));

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pub fn rem_euclid(self, rhs: Self) -> Self

Calculates the least remainder of self (mod rhs).

Since, for the positive integers, all common definitions of division are equal, this is exactly equal to self % rhs.

Panics

This function will panic if rhs is 0.

Examples

Basic usage:

assert_eq!(U256::new(7).rem_euclid(U256::new(4)), U256::new(3));

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pub fn is_power_of_two(self) -> bool

Returns true if and only if self == 2^k for some k.

Examples

Basic usage:

assert!(U256::new(16).is_power_of_two());
assert!(!U256::new(10).is_power_of_two());

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pub fn next_power_of_two(self) -> Self

Returns the smallest power of two greater than or equal to self.

When return value overflows (i.e., self > (1 << (N-1)) for type uN), it panics in debug mode and return value is wrapped to 0 in release mode (the only situation in which method can return 0).

Examples

Basic usage:

assert_eq!(U256::new(2).next_power_of_two(), U256::new(2));
assert_eq!(U256::new(3).next_power_of_two(), U256::new(4));

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pub fn checked_next_power_of_two(self) -> Option<Self>

Returns the smallest power of two greater than or equal to n. If the next power of two is greater than the type’s maximum value, None is returned, otherwise the power of two is wrapped in Some.

Examples

Basic usage:

assert_eq!(U256::new(2).checked_next_power_of_two(), Some(U256::new(2)));
assert_eq!(U256::new(3).checked_next_power_of_two(), Some(U256::new(4)));
assert_eq!(U256::MAX.checked_next_power_of_two(), None);

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pub fn to_be_bytes(self) -> [u8; 32]

Return the memory representation of this integer as a byte array in big endian (network) byte order.

Examples

let bytes = U256::from_words(
    0x00010203_04050607_08090a0b_0c0d0e0f,
    0x10111213_14151617_18191a1b_1c1d1e1f,
);
assert_eq!(
    bytes.to_be_bytes(),
    [
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
        0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
    ],
);

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pub fn to_le_bytes(self) -> [u8; 32]

Return the memory representation of this integer as a byte array in little endian byte order.

Examples

let bytes = U256::from_words(
    0x00010203_04050607_08090a0b_0c0d0e0f,
    0x10111213_14151617_18191a1b_1c1d1e1f,
);
assert_eq!(
    bytes.to_le_bytes(),
    [
        0x1f, 0x1e, 0x1d, 0x1c, 0x1b, 0x1a, 0x19, 0x18, 0x17, 0x16, 0x15, 0x14, 0x13, 0x12, 0x11, 0x10,
        0x0f, 0x0e, 0x0d, 0x0c, 0x0b, 0x0a, 0x09, 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01, 0x00,
    ],
);

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pub fn to_ne_bytes(self) -> [u8; 32]

Return the memory representation of this integer as a byte array in native byte order.

As the target platform’s native endianness is used, portable code should use to_be_bytes or to_le_bytes, as appropriate, instead.

Examples

let bytes = U256::from_words(
    0x00010203_04050607_08090a0b_0c0d0e0f,
    0x10111213_14151617_18191a1b_1c1d1e1f,
);
assert_eq!(
    bytes.to_ne_bytes(),
    if cfg!(target_endian = "big") {
        [
            0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
            0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
        ]
    } else {
        [
            0x1f, 0x1e, 0x1d, 0x1c, 0x1b, 0x1a, 0x19, 0x18, 0x17, 0x16, 0x15, 0x14, 0x13, 0x12, 0x11, 0x10,
            0x0f, 0x0e, 0x0d, 0x0c, 0x0b, 0x0a, 0x09, 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01, 0x00,
        ]
    }
);

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pub fn from_be_bytes(bytes: [u8; 32]) -> Self

Create an integer value from its representation as a byte array in big endian.

Examples

let value = U256::from_be_bytes([
    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
    0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
]);
assert_eq!(
    value,
    U256::from_words(
        0x00010203_04050607_08090a0b_0c0d0e0f,
        0x10111213_14151617_18191a1b_1c1d1e1f,
    ),
);

When starting from a slice rather than an array, fallible conversion APIs can be used:

use std::convert::TryInto;

fn read_be_u256(input: &mut &[u8]) -> U256 {
    let (int_bytes, rest) = input.split_at(std::mem::size_of::<U256>());
    *input = rest;
    U256::from_be_bytes(int_bytes.try_into().unwrap())
}

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pub fn from_le_bytes(bytes: [u8; 32]) -> Self

Create an integer value from its representation as a byte array in little endian.

Examples

let value = U256::from_le_bytes([
    0x1f, 0x1e, 0x1d, 0x1c, 0x1b, 0x1a, 0x19, 0x18, 0x17, 0x16, 0x15, 0x14, 0x13, 0x12, 0x11, 0x10,
    0x0f, 0x0e, 0x0d, 0x0c, 0x0b, 0x0a, 0x09, 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01, 0x00,
]);
assert_eq!(
    value,
    U256::from_words(
        0x00010203_04050607_08090a0b_0c0d0e0f,
        0x10111213_14151617_18191a1b_1c1d1e1f,
    ),
);

When starting from a slice rather than an array, fallible conversion APIs can be used:

use std::convert::TryInto;

fn read_be_u256(input: &mut &[u8]) -> U256 {
    let (int_bytes, rest) = input.split_at(std::mem::size_of::<U256>());
    *input = rest;
    U256::from_le_bytes(int_bytes.try_into().unwrap())
}

source

pub fn from_ne_bytes(bytes: [u8; 32]) -> Self

Create an integer value from its memory representation as a byte array in native endianness.

As the target platform’s native endianness is used, portable code likely wants to use from_be_bytes or from_le_bytes, as appropriate instead.

Examples

let value = U256::from_ne_bytes(if cfg!(target_endian = "big") {
    [
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
        0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
    ]
} else {
    [
        0x1f, 0x1e, 0x1d, 0x1c, 0x1b, 0x1a, 0x19, 0x18, 0x17, 0x16, 0x15, 0x14, 0x13, 0x12, 0x11, 0x10,
        0x0f, 0x0e, 0x0d, 0x0c, 0x0b, 0x0a, 0x09, 0x08, 0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01, 0x00,
    ]
});
assert_eq!(
    value,
    U256::from_words(
        0x00010203_04050607_08090a0b_0c0d0e0f,
        0x10111213_14151617_18191a1b_1c1d1e1f,
    ),
);

When starting from a slice rather than an array, fallible conversion APIs can be used:

use std::convert::TryInto;

fn read_be_u256(input: &mut &[u8]) -> U256 {
    let (int_bytes, rest) = input.split_at(std::mem::size_of::<U256>());
    *input = rest;
    U256::from_ne_bytes(int_bytes.try_into().unwrap())
}

source §

Converts a prefixed string slice in base 16 to an integer.

The string is expected to be an optional + sign followed by the 0x prefix and finally the digits. Leading and trailing whitespace represent an error.

Examples

Basic usage:

assert_eq!(U256::from_str_hex("0x2A"), Ok(U256::new(42)));

source

pub fn from_str_prefixed(src: &str) -> Result<Self, ParseIntError>

Converts a prefixed string slice in a base determined by the prefix to an integer.

The string is expected to be an optional + sign followed by the one of the supported prefixes and finally the digits. Leading and trailing whitespace represent an error. The base is determined based on the prefix:

0b: base 2
0o: base 8
0x: base 16
no prefix: base 10

Examples

Basic usage:

assert_eq!(U256::from_str_prefixed("0b101"), Ok(U256::new(0b101)));
assert_eq!(U256::from_str_prefixed("0o17"), Ok(U256::new(0o17)));
assert_eq!(U256::from_str_prefixed("0xa"), Ok(U256::new(0xa)));
assert_eq!(U256::from_str_prefixed("42"), Ok(U256::new(42)));