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u256.move
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u256.move
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// SPDX-License-Identifier: Apache-2.0
// Copied from: https://github.com/pontem-network/U256/blob/main/sources/u256.move
/// @title u256
/// @dev The implementation of large numbers written in Move language.
/// Code derived from original work by Andrew Poelstra <apoelstra@wpsoftware.net>
///
/// Rust Bitcoin Library
/// Written in 2014 by
/// Andrew Poelstra <apoelstra@wpsoftware.net>
///
/// To the extent possible under law, the author(s) have dedicated all
/// copyright and related and neighboring rights to this software to
/// the public domain worldwide. This software is distributed without
/// any warranty.
///
/// Simplified impl by Parity Team - https://github.com/paritytech/parity-common/blob/master/uint/src/uint.rs
///
/// Features:
/// * mul
/// * div
/// * add
/// * sub
/// * shift left
/// * shift right
/// * compare
/// * if math overflows the contract crashes.
///
/// Would be nice to help with the following TODO list:
/// * pow() , sqrt().
/// * math funcs that don't abort on overflows, but just returns reminders.
/// * Export of low_u128 (see original implementation).
/// * Export of low_u64 (see original implementation).
/// * Gas Optimisation:
/// * We can optimize by replacing bytecode, as far as we know Move VM itself support slices, so probably
/// we can try to replace parts works with (`v0`,`v1`,`v2`,`v3` etc) works.
/// * More?
/// * More tests (see current tests and TODOs i left):
/// * u256_arithmetic_test - https://github.com/paritytech/bigint/blob/master/src/uint.rs#L1338
/// * More from - https://github.com/paritytech/bigint/blob/master/src/uint.rs
/// * Division:
/// * Could be improved with div_mod_small (current version probably would took a lot of resources for small numbers).
/// * Also could be improved with Knuth, TAOCP, Volume 2, section 4.3.1, Algorithm D (see link to Parity above).
module pancake::u256 {
use std::bcs;
use std::vector;
// Errors.
/// When can't cast `U256` to `u128` (e.g. number too large).
const ECAST_OVERFLOW: u64 = 0;
/// When trying to get or put word into U256 but it's out of index.
const EWORDS_OVERFLOW: u64 = 1;
/// When math overflows.
const EOVERFLOW: u64 = 2;
/// When attempted to divide by zero.
const EDIV_BY_ZERO: u64 = 3;
/// When trying to call `from_bytes` on a vector of length != 32.
const EVECTOR_LENGTH_NOT_32_BYTES: u64 = 4;
// Constants.
/// Max `u64` value.
const U64_MAX: u128 = 18446744073709551615;
/// Max `u128` value.
const U128_MAX: u128 = 340282366920938463463374607431768211455;
/// Total words in `U256` (64 * 4 = 256).
const WORDS: u64 = 4;
/// When both `U256` equal.
const EQUAL: u8 = 0;
/// When `a` is less than `b`.
const LESS_THAN: u8 = 1;
/// When `b` is greater than `b`.
const GREATER_THAN: u8 = 2;
// Data structs.
/// The `U256` resource.
/// Contains 4 u64 numbers.
struct U256 has copy, drop, store {
v0: u64,
v1: u64,
v2: u64,
v3: u64,
}
/// Double `U256` used for multiple (to store overflow).
struct DU256 has copy, drop, store {
v0: u64,
v1: u64,
v2: u64,
v3: u64,
v4: u64,
v5: u64,
v6: u64,
v7: u64,
}
// Public functions.
/// Adds two `U256` and returns sum.
public fun add(a: U256, b: U256): U256 {
let ret = zero();
let carry = 0u64;
let i = 0;
while (i < WORDS) {
let a1 = get(&a, i);
let b1 = get(&b, i);
if (carry != 0) {
let (res1, is_overflow1) = overflowing_add(a1, b1);
let (res2, is_overflow2) = overflowing_add(res1, carry);
put(&mut ret, i, res2);
carry = 0;
if (is_overflow1) {
carry = carry + 1;
};
if (is_overflow2) {
carry = carry + 1;
}
} else {
let (res, is_overflow) = overflowing_add(a1, b1);
put(&mut ret, i, res);
carry = 0;
if (is_overflow) {
carry = 1;
};
};
i = i + 1;
};
assert!(carry == 0, EOVERFLOW);
ret
}
/// Convert `U256` to `u128` value if possible (otherwise it aborts).
public fun as_u128(a: U256): u128 {
assert!(a.v2 == 0 && a.v3 == 0, ECAST_OVERFLOW);
((a.v1 as u128) << 64) + (a.v0 as u128)
}
/// Convert `U256` to `u64` value if possible (otherwise it aborts).
public fun as_u64(a: U256): u64 {
assert!(a.v1 == 0 && a.v2 == 0 && a.v3 == 0, ECAST_OVERFLOW);
a.v0
}
/// Compares two `U256` numbers.
public fun compare(a: &U256, b: &U256): u8 {
let i = WORDS;
while (i > 0) {
i = i - 1;
let a1 = get(a, i);
let b1 = get(b, i);
if (a1 != b1) {
if (a1 < b1) {
return LESS_THAN
} else {
return GREATER_THAN
}
}
};
EQUAL
}
/// Returns a `U256` from `u64` value.
public fun from_u64(val: u64): U256 {
from_u128((val as u128))
}
/// Returns a `U256` from `u128` value.
public fun from_u128(val: u128): U256 {
let (a2, a1) = split_u128(val);
U256 {
v0: a1,
v1: a2,
v2: 0,
v3: 0,
}
}
/// Multiples two `U256`.
public fun mul(a: U256, b: U256): U256 {
let ret = DU256 {
v0: 0,
v1: 0,
v2: 0,
v3: 0,
v4: 0,
v5: 0,
v6: 0,
v7: 0,
};
let i = 0;
while (i < WORDS) {
let carry = 0u64;
let b1 = get(&b, i);
let j = 0;
while (j < WORDS) {
let a1 = get(&a, j);
if (a1 != 0 || carry != 0) {
let (hi, low) = split_u128((a1 as u128) * (b1 as u128));
let overflow = {
let existing_low = get_d(&ret, i + j);
let (low, o) = overflowing_add(low, existing_low);
put_d(&mut ret, i + j, low);
if (o) {
1
} else {
0
}
};
carry = {
let existing_hi = get_d(&ret, i + j + 1);
let hi = hi + overflow;
let (hi, o0) = overflowing_add(hi, carry);
let (hi, o1) = overflowing_add(hi, existing_hi);
put_d(&mut ret, i + j + 1, hi);
if (o0 || o1) {
1
} else {
0
}
};
};
j = j + 1;
};
i = i + 1;
};
let (r, overflow) = du256_to_u256(ret);
assert!(!overflow, EOVERFLOW);
r
}
/// Subtracts two `U256`, returns result.
public fun sub(a: U256, b: U256): U256 {
let ret = zero();
let carry = 0u64;
let i = 0;
while (i < WORDS) {
let a1 = get(&a, i);
let b1 = get(&b, i);
if (carry != 0) {
let (res1, is_overflow1) = overflowing_sub(a1, b1);
let (res2, is_overflow2) = overflowing_sub(res1, carry);
put(&mut ret, i, res2);
carry = 0;
if (is_overflow1) {
carry = carry + 1;
};
if (is_overflow2) {
carry = carry + 1;
}
} else {
let (res, is_overflow) = overflowing_sub(a1, b1);
put(&mut ret, i, res);
carry = 0;
if (is_overflow) {
carry = 1;
};
};
i = i + 1;
};
assert!(carry == 0, EOVERFLOW);
ret
}
/// Divide `a` by `b`.
public fun div(a: U256, b: U256): U256 {
let ret = zero();
let a_bits = bits(&a);
let b_bits = bits(&b);
assert!(b_bits != 0, EDIV_BY_ZERO); // DIVIDE BY ZERO.
if (a_bits < b_bits) {
// Immidiatelly return.
return ret
};
let shift = a_bits - b_bits;
b = shl(b, (shift as u8));
loop {
let cmp = compare(&a, &b);
if (cmp == GREATER_THAN || cmp == EQUAL) {
let index = shift / 64;
let m = get(&ret, index);
let c = m | 1 << ((shift % 64) as u8);
put(&mut ret, index, c);
a = sub(a, b);
};
b = shr(b, 1);
if (shift == 0) {
break
};
shift = shift - 1;
};
ret
}
/// Shift right `a` by `shift`.
public fun shr(a: U256, shift: u8): U256 {
let ret = zero();
let word_shift = (shift as u64) / 64;
let bit_shift = (shift as u64) % 64;
let i = word_shift;
while (i < WORDS) {
let m = get(&a, i) >> (bit_shift as u8);
put(&mut ret, i - word_shift, m);
i = i + 1;
};
if (bit_shift > 0) {
let j = word_shift + 1;
while (j < WORDS) {
let m = get(&ret, j - word_shift - 1) + (get(&a, j) << (64 - (bit_shift as u8)));
put(&mut ret, j - word_shift - 1, m);
j = j + 1;
};
};
ret
}
/// Shift left `a` by `shift`.
public fun shl(a: U256, shift: u8): U256 {
let ret = zero();
let word_shift = (shift as u64) / 64;
let bit_shift = (shift as u64) % 64;
let i = word_shift;
while (i < WORDS) {
let m = get(&a, i - word_shift) << (bit_shift as u8);
put(&mut ret, i, m);
i = i + 1;
};
if (bit_shift > 0) {
let j = word_shift + 1;
while (j < WORDS) {
let m = get(&ret, j) + (get(&a, j - 1 - word_shift) >> (64 - (bit_shift as u8)));
put(&mut ret, j, m);
j = j + 1;
};
};
ret
}
/// Returns `a` AND `b`.
public fun and(a: &U256, b: &U256): U256 {
let ret = zero();
let i = 0;
while (i < WORDS) {
let m = get(a, i) & get(b, i);
put(&mut ret, i, m);
i = i + 1;
};
ret
}
/// Returns `a` OR `b`.
public fun or(a: &U256, b: &U256): U256 {
let ret = zero();
let i = 0;
while (i < WORDS) {
let m = get(a, i) | get(b, i);
put(&mut ret, i, m);
i = i + 1;
};
ret
}
/// Returns `a` XOR `b`.
public fun xor(a: &U256, b: &U256): U256 {
let ret = zero();
let i = 0;
while (i < WORDS) {
let m = get(a, i) ^ get(b, i);
put(&mut ret, i, m);
i = i + 1;
};
ret
}
/// Returns `U256` equals to zero.
public fun zero(): U256 {
U256 {
v0: 0,
v1: 0,
v2: 0,
v3: 0,
}
}
// Private functions.
/// Get bits used to store `a`.
fun bits(a: &U256): u64 {
let i = 1;
while (i < WORDS) {
let a1 = get(a, WORDS - i);
if (a1 > 0) {
return ((0x40 * (WORDS - i + 1)) - (leading_zeros_u64(a1) as u64))
};
i = i + 1;
};
let a1 = get(a, 0);
0x40 - (leading_zeros_u64(a1) as u64)
}
/// Get leading zeros of a binary representation of `a`.
fun leading_zeros_u64(a: u64): u8 {
if (a == 0) {
return 64
};
let a1 = a & 0xFFFFFFFF;
let a2 = a >> 32;
if (a2 == 0) {
let bit = 32;
while (bit >= 1) {
let b = (a1 >> (bit - 1)) & 1;
if (b != 0) {
break
};
bit = bit - 1;
};
(32 - bit) + 32
} else {
let bit = 64;
while (bit >= 1) {
let b = (a >> (bit - 1)) & 1;
if (b != 0) {
break
};
bit = bit - 1;
};
64 - bit
}
}
/// Similar to Rust `overflowing_add`.
/// 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.
fun overflowing_add(a: u64, b: u64): (u64, bool) {
let a128 = (a as u128);
let b128 = (b as u128);
let r = a128 + b128;
if (r > U64_MAX) {
// overflow
let overflow = r - U64_MAX - 1;
((overflow as u64), true)
} else {
(((a128 + b128) as u64), false)
}
}
/// Similar to Rust `overflowing_sub`.
/// 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.
fun overflowing_sub(a: u64, b: u64): (u64, bool) {
if (a < b) {
let r = b - a;
((U64_MAX as u64) - r + 1, true)
} else {
(a - b, false)
}
}
/// Extracts two `u64` from `a` `u128`.
fun split_u128(a: u128): (u64, u64) {
let a1 = ((a >> 64) as u64);
let a2 = ((a & 0xFFFFFFFFFFFFFFFF) as u64);
(a1, a2)
}
/// Get word from `a` by index `i`.
public fun get(a: &U256, i: u64): u64 {
if (i == 0) {
a.v0
} else if (i == 1) {
a.v1
} else if (i == 2) {
a.v2
} else if (i == 3) {
a.v3
} else {
abort EWORDS_OVERFLOW
}
}
/// Get word from `DU256` by index.
fun get_d(a: &DU256, i: u64): u64 {
if (i == 0) {
a.v0
} else if (i == 1) {
a.v1
} else if (i == 2) {
a.v2
} else if (i == 3) {
a.v3
} else if (i == 4) {
a.v4
} else if (i == 5) {
a.v5
} else if (i == 6) {
a.v6
} else if (i == 7) {
a.v7
} else {
abort EWORDS_OVERFLOW
}
}
/// Put new word `val` into `U256` by index `i`.
fun put(a: &mut U256, i: u64, val: u64) {
if (i == 0) {
a.v0 = val;
} else if (i == 1) {
a.v1 = val;
} else if (i == 2) {
a.v2 = val;
} else if (i == 3) {
a.v3 = val;
} else {
abort EWORDS_OVERFLOW
}
}
/// Put new word into `DU256` by index `i`.
fun put_d(a: &mut DU256, i: u64, val: u64) {
if (i == 0) {
a.v0 = val;
} else if (i == 1) {
a.v1 = val;
} else if (i == 2) {
a.v2 = val;
} else if (i == 3) {
a.v3 = val;
} else if (i == 4) {
a.v4 = val;
} else if (i == 5) {
a.v5 = val;
} else if (i == 6) {
a.v6 = val;
} else if (i == 7) {
a.v7 = val;
} else {
abort EWORDS_OVERFLOW
}
}
/// Convert `DU256` to `U256`.
fun du256_to_u256(a: DU256): (U256, bool) {
let b = U256 {
v0: a.v0,
v1: a.v1,
v2: a.v2,
v3: a.v3,
};
let overflow = false;
if (a.v4 != 0 || a.v5 != 0 || a.v6 != 0 || a.v7 != 0) {
overflow = true;
};
(b, overflow)
}
/// Converts `vector<u8>` `a` to a `U256`.
public fun from_bytes(a: &vector<u8>): U256 {
assert!(vector::length(a) == 32, EVECTOR_LENGTH_NOT_32_BYTES);
let ret = zero();
put(&mut ret, 0, ((*vector::borrow(a, 0) as u64) << 7) + ((*vector::borrow(a, 1) as u64) << 6)
+ ((*vector::borrow(a, 2) as u64) << 5) + ((*vector::borrow(a, 3) as u64) << 4)
+ ((*vector::borrow(a, 4) as u64) << 3) + ((*vector::borrow(a, 5) as u64) << 2)
+ ((*vector::borrow(a, 6) as u64) << 1) + (*vector::borrow(a, 7) as u64));
put(&mut ret, 1, ((*vector::borrow(a, 8) as u64) << 7) + ((*vector::borrow(a, 9) as u64) << 6)
+ ((*vector::borrow(a, 10) as u64) << 5) + ((*vector::borrow(a, 11) as u64) << 4)
+ ((*vector::borrow(a, 12) as u64) << 3) + ((*vector::borrow(a, 13) as u64) << 2)
+ ((*vector::borrow(a, 14) as u64) << 1) + (*vector::borrow(a, 15) as u64));
put(&mut ret, 2, ((*vector::borrow(a, 16) as u64) << 7) + ((*vector::borrow(a, 17) as u64) << 6)
+ ((*vector::borrow(a, 18) as u64) << 5) + ((*vector::borrow(a, 19) as u64) << 4)
+ ((*vector::borrow(a, 20) as u64) << 3) + ((*vector::borrow(a, 21) as u64) << 2)
+ ((*vector::borrow(a, 22) as u64) << 1) + (*vector::borrow(a, 23) as u64));
put(&mut ret, 3, ((*vector::borrow(a, 24) as u64) << 7) + ((*vector::borrow(a, 25) as u64) << 6)
+ ((*vector::borrow(a, 26) as u64) << 5) + ((*vector::borrow(a, 27) as u64) << 4)
+ ((*vector::borrow(a, 28) as u64) << 3) + ((*vector::borrow(a, 29) as u64) << 2)
+ ((*vector::borrow(a, 30) as u64) << 1) + (*vector::borrow(a, 31) as u64));
ret
}
/// Converts `U256` `a` to a `vector<u8>`.
public fun to_bytes(a: &U256): vector<u8> {
let ret = vector::empty<u8>();
vector::append(&mut ret, bcs::to_bytes(&get(a, 0)));
vector::append(&mut ret, bcs::to_bytes(&get(a, 1)));
vector::append(&mut ret, bcs::to_bytes(&get(a, 2)));
vector::append(&mut ret, bcs::to_bytes(&get(a, 3)));
ret
}
public fun get_equal(): u8 {
EQUAL
}
public fun get_less_than(): u8 {
LESS_THAN
}
public fun get_greater_than(): u8 {
GREATER_THAN
}
// Tests.
#[test]
fun test_get_d() {
let a = DU256 {
v0: 1,
v1: 2,
v2: 3,
v3: 4,
v4: 5,
v5: 6,
v6: 7,
v7: 8,
};
assert!(get_d(&a, 0) == 1, 0);
assert!(get_d(&a, 1) == 2, 1);
assert!(get_d(&a, 2) == 3, 2);
assert!(get_d(&a, 3) == 4, 3);
assert!(get_d(&a, 4) == 5, 4);
assert!(get_d(&a, 5) == 6, 5);
assert!(get_d(&a, 6) == 7, 6);
assert!(get_d(&a, 7) == 8, 7);
}
#[test]
#[expected_failure(abort_code = 1)]
fun test_get_d_overflow() {
let a = DU256 {
v0: 1,
v1: 2,
v2: 3,
v3: 4,
v4: 5,
v5: 6,
v6: 7,
v7: 8,
};
get_d(&a, 8);
}
#[test]
fun test_put_d() {
let a = DU256 {
v0: 1,
v1: 2,
v2: 3,
v3: 4,
v4: 5,
v5: 6,
v6: 7,
v7: 8,
};
put_d(&mut a, 0, 10);
put_d(&mut a, 1, 20);
put_d(&mut a, 2, 30);
put_d(&mut a, 3, 40);
put_d(&mut a, 4, 50);
put_d(&mut a, 5, 60);
put_d(&mut a, 6, 70);
put_d(&mut a, 7, 80);
assert!(get_d(&a, 0) == 10, 0);
assert!(get_d(&a, 1) == 20, 1);
assert!(get_d(&a, 2) == 30, 2);
assert!(get_d(&a, 3) == 40, 3);
assert!(get_d(&a, 4) == 50, 4);
assert!(get_d(&a, 5) == 60, 5);
assert!(get_d(&a, 6) == 70, 6);
assert!(get_d(&a, 7) == 80, 7);
}
#[test]
#[expected_failure(abort_code = 1)]
fun test_put_d_overflow() {
let a = DU256 {
v0: 1,
v1: 2,
v2: 3,
v3: 4,
v4: 5,
v5: 6,
v6: 7,
v7: 8,
};
put_d(&mut a, 8, 0);
}
#[test]
fun test_du256_to_u256() {
let a = DU256 {
v0: 255,
v1: 100,
v2: 50,
v3: 300,
v4: 0,
v5: 0,
v6: 0,
v7: 0,
};
let (m, overflow) = du256_to_u256(a);
assert!(!overflow, 0);
assert!(m.v0 == a.v0, 1);
assert!(m.v1 == a.v1, 2);
assert!(m.v2 == a.v2, 3);
assert!(m.v3 == a.v3, 4);
a.v4 = 100;
a.v5 = 5;
let (m, overflow) = du256_to_u256(a);
assert!(overflow, 5);
assert!(m.v0 == a.v0, 6);
assert!(m.v1 == a.v1, 7);
assert!(m.v2 == a.v2, 8);
assert!(m.v3 == a.v3, 9);
}
#[test]
fun test_get() {
let a = U256 {
v0: 1,
v1: 2,
v2: 3,
v3: 4,
};
assert!(get(&a, 0) == 1, 0);
assert!(get(&a, 1) == 2, 1);
assert!(get(&a, 2) == 3, 2);
assert!(get(&a, 3) == 4, 3);
}
#[test]
#[expected_failure(abort_code = 1)]
fun test_get_aborts() {
let _ = get(&zero(), 4);
}
#[test]
fun test_put() {
let a = zero();
put(&mut a, 0, 255);
assert!(get(&a, 0) == 255, 0);
put(&mut a, 1, (U64_MAX as u64));
assert!(get(&a, 1) == (U64_MAX as u64), 1);
put(&mut a, 2, 100);
assert!(get(&a, 2) == 100, 2);
put(&mut a, 3, 3);
assert!(get(&a, 3) == 3, 3);
put(&mut a, 2, 0);
assert!(get(&a, 2) == 0, 4);
}
#[test]
#[expected_failure(abort_code = 1)]
fun test_put_overflow() {
let a = zero();
put(&mut a, 6, 255);
}
#[test]
fun test_from_u128() {
let i = 0;
while (i < 1024) {
let big = from_u128(i);
assert!(as_u128(big) == i, 0);
i = i + 1;
};
}
#[test]
fun test_add() {
let a = from_u128(1000);
let b = from_u128(500);
let s = as_u128(add(a, b));
assert!(s == 1500, 0);
a = from_u128(U64_MAX);
b = from_u128(U64_MAX);
s = as_u128(add(a, b));
assert!(s == (U64_MAX + U64_MAX), 1);
}
#[test]
#[expected_failure(abort_code = 2)]
fun test_add_overflow() {
let max = (U64_MAX as u64);
let a = U256 {
v0: max,
v1: max,
v2: max,
v3: max
};
let _ = add(a, from_u128(1));
}
#[test]
fun test_sub() {
let a = from_u128(1000);
let b = from_u128(500);
let s = as_u128(sub(a, b));
assert!(s == 500, 0);
}
#[test]
#[expected_failure(abort_code = 2)]
fun test_sub_overflow() {
let a = from_u128(0);
let b = from_u128(1);
let _ = sub(a, b);
}
#[test]
#[expected_failure(abort_code = 0)]
fun test_too_big_to_cast_to_u128() {
let a = from_u128(U128_MAX);
let b = from_u128(U128_MAX);
let _ = as_u128(add(a, b));
}
#[test]
fun test_overflowing_add() {
let (n, z) = overflowing_add(10, 10);
assert!(n == 20, 0);
assert!(!z, 1);
(n, z) = overflowing_add((U64_MAX as u64), 1);
assert!(n == 0, 2);
assert!(z, 3);
(n, z) = overflowing_add((U64_MAX as u64), 10);
assert!(n == 9, 4);
assert!(z, 5);
(n, z) = overflowing_add(5, 8);
assert!(n == 13, 6);
assert!(!z, 7);
}
#[test]
fun test_overflowing_sub() {
let (n, z) = overflowing_sub(10, 5);
assert!(n == 5, 0);
assert!(!z, 1);
(n, z) = overflowing_sub(0, 1);
assert!(n == (U64_MAX as u64), 2);
assert!(z, 3);
(n, z) = overflowing_sub(10, 10);
assert!(n == 0, 4);
assert!(!z, 5);
}
#[test]
fun test_split_u128() {
let (a1, a2) = split_u128(100);
assert!(a1 == 0, 0);
assert!(a2 == 100, 1);
(a1, a2) = split_u128(U64_MAX + 1);
assert!(a1 == 1, 2);
assert!(a2 == 0, 3);
}
#[test]
fun test_mul() {
let a = from_u128(285);
let b = from_u128(375);
let c = as_u128(mul(a, b));
assert!(c == 106875, 0);
a = from_u128(0);
b = from_u128(1);
c = as_u128(mul(a, b));
assert!(c == 0, 1);
a = from_u128(U64_MAX);
b = from_u128(2);
c = as_u128(mul(a, b));
assert!(c == 36893488147419103230, 2);
a = from_u128(U128_MAX);
b = from_u128(U128_MAX);
let z = mul(a, b);
assert!(bits(&z) == 256, 3);
}
#[test]
#[expected_failure(abort_code = 2)]
fun test_mul_overflow() {
let max = (U64_MAX as u64);
let a = U256 {
v0: max,
v1: max,
v2: max,
v3: max,
};
let _ = mul(a, from_u128(2));
}
#[test]
fun test_zero() {
let a = as_u128(zero());
assert!(a == 0, 0);