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Add carrying_add, borrowing_sub, widening_mul, carrying_mul methods t…
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…o integers
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clarfonthey committed Aug 26, 2021
1 parent ad02dc4 commit cc15047
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1 change: 1 addition & 0 deletions library/core/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,7 @@
#![feature(const_alloc_layout)]
#![feature(const_arguments_as_str)]
#![feature(const_assert_type)]
#![feature(const_bigint_helper_methods)]
#![feature(const_caller_location)]
#![feature(const_cell_into_inner)]
#![feature(const_discriminant)]
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54 changes: 54 additions & 0 deletions library/core/src/num/int_macros.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1307,6 +1307,33 @@ macro_rules! int_impl {
(a as Self, b)
}

/// Calculates `self + rhs + carry` without the ability to overflow.
///
/// Performs "ternary addition" which takes in an extra bit to add, and may return an
/// additional bit of overflow. This allows for chaining together multiple additions
/// to create "big integers" which represent larger values.
///
/// # Examples
///
/// Basic usage
///
/// ```
/// #![feature(bigint_helper_methods)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".carrying_add(2, false), (7, false));")]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".carrying_add(2, true), (8, false));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, false), (", stringify!($SelfT), "::MIN, false));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, true), (", stringify!($SelfT), "::MIN + 1, false));")]
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn carrying_add(self, rhs: Self, carry: bool) -> (Self, bool) {
let (sum, carry) = (self as $UnsignedT).carrying_add(rhs as $UnsignedT, carry);
(sum as $SelfT, carry)
}

/// Calculates `self` - `rhs`
///
/// Returns a tuple of the subtraction along with a boolean indicating whether an arithmetic overflow
Expand All @@ -1331,6 +1358,33 @@ macro_rules! int_impl {
(a as Self, b)
}

/// Calculates `self - rhs - borrow` without the ability to overflow.
///
/// Performs "ternary subtraction" which takes in an extra bit to subtract, and may return
/// an additional bit of overflow. This allows for chaining together multiple subtractions
/// to create "big integers" which represent larger values.
///
/// # Examples
///
/// Basic usage
///
/// ```
/// #![feature(bigint_helper_methods)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".borrowing_sub(2, false), (3, false));")]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".borrowing_sub(2, true), (2, false));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.borrowing_sub(1, false), (", stringify!($SelfT), "::MAX, false));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MIN.borrowing_sub(1, true), (", stringify!($SelfT), "::MAX - 1, false));")]
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn borrowing_sub(self, rhs: Self, borrow: bool) -> (Self, bool) {
let (sum, borrow) = (self as $UnsignedT).borrowing_sub(rhs as $UnsignedT, borrow);
(sum as $SelfT, borrow)
}

/// Calculates the multiplication of `self` and `rhs`.
///
/// Returns a tuple of the multiplication along with a boolean indicating whether an arithmetic overflow
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87 changes: 87 additions & 0 deletions library/core/src/num/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -89,27 +89,104 @@ depending on the target pointer size.
};
}

macro_rules! widening_impl {
($SelfT:ty, $WideT:ty, $BITS:literal) => {
/// Calculates the complete product `self * rhs` without the possibility to overflow.
///
/// This returns the low-order (wrapping) bits and the high-order (overflow) bits
/// of the result as two separate values, in that order.
///
/// # Examples
///
/// Basic usage:
///
/// Please note that this example is shared between integer types.
/// Which explains why `u32` is used here.
///
/// ```
/// #![feature(bigint_helper_methods)]
/// assert_eq!(5u32.widening_mul(2), (10, 0));
/// assert_eq!(1_000_000_000u32.widening_mul(10), (1410065408, 2));
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn widening_mul(self, rhs: Self) -> (Self, Self) {
// note: longer-term this should be done via an intrinsic,
// but for now we can deal without an impl for u128/i128
// SAFETY: overflow will be contained within the wider types
let wide = unsafe { (self as $WideT).unchecked_mul(rhs as $WideT) };
(wide as $SelfT, (wide >> $BITS) as $SelfT)
}

/// Calculates the "full multiplication" `self * rhs + carry`
/// without the possibility to overflow.
///
/// This returns the low-order (wrapping) bits and the high-order (overflow) bits
/// of the result as two separate values, in that order.
///
/// Performs "long multiplication" which takes in an extra amount to add, and may return an
/// additional amount of overflow. This allows for chaining together multiple
/// multiplications to create "big integers" which represent larger values.
///
/// # Examples
///
/// Basic usage:
///
/// Please note that this example is shared between integer types.
/// Which explains why `u32` is used here.
///
/// ```
/// #![feature(bigint_helper_methods)]
/// assert_eq!(5u32.carrying_mul(2, 0), (10, 0));
/// assert_eq!(5u32.carrying_mul(2, 10), (20, 0));
/// assert_eq!(1_000_000_000u32.carrying_mul(10, 0), (1410065408, 2));
/// assert_eq!(1_000_000_000u32.carrying_mul(10, 10), (1410065418, 2));
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "bigint_helper_methods", issue = "85532")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn carrying_mul(self, rhs: Self, carry: Self) -> (Self, Self) {
// note: longer-term this should be done via an intrinsic,
// but for now we can deal without an impl for u128/i128
// SAFETY: overflow will be contained within the wider types
let wide = unsafe {
(self as $WideT).unchecked_mul(rhs as $WideT).unchecked_add(carry as $WideT)
};
(wide as $SelfT, (wide >> $BITS) as $SelfT)
}
};
}

#[lang = "i8"]
impl i8 {
widening_impl! { i8, i16, 8 }
int_impl! { i8, i8, u8, 8, 7, -128, 127, 2, "-0x7e", "0xa", "0x12", "0x12", "0x48",
"[0x12]", "[0x12]", "", "" }
}

#[lang = "i16"]
impl i16 {
widening_impl! { i16, i32, 16 }
int_impl! { i16, i16, u16, 16, 15, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234", "0x3412",
"0x2c48", "[0x34, 0x12]", "[0x12, 0x34]", "", "" }
}

#[lang = "i32"]
impl i32 {
widening_impl! { i32, i64, 32 }
int_impl! { i32, i32, u32, 32, 31, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
"0x12345678", "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]",
"[0x12, 0x34, 0x56, 0x78]", "", "" }
}

#[lang = "i64"]
impl i64 {
widening_impl! { i64, i128, 64 }
int_impl! { i64, i64, u64, 64, 63, -9223372036854775808, 9223372036854775807, 12,
"0xaa00000000006e1", "0x6e10aa", "0x1234567890123456", "0x5634129078563412",
"0x6a2c48091e6a2c48", "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
Expand All @@ -131,6 +208,7 @@ impl i128 {
#[cfg(target_pointer_width = "16")]
#[lang = "isize"]
impl isize {
widening_impl! { isize, i32, 16 }
int_impl! { isize, i16, usize, 16, 15, -32768, 32767, 4, "-0x5ffd", "0x3a", "0x1234",
"0x3412", "0x2c48", "[0x34, 0x12]", "[0x12, 0x34]",
usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!() }
Expand All @@ -139,6 +217,7 @@ impl isize {
#[cfg(target_pointer_width = "32")]
#[lang = "isize"]
impl isize {
widening_impl! { isize, i64, 32 }
int_impl! { isize, i32, usize, 32, 31, -2147483648, 2147483647, 8, "0x10000b3", "0xb301",
"0x12345678", "0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]",
"[0x12, 0x34, 0x56, 0x78]",
Expand All @@ -148,6 +227,7 @@ impl isize {
#[cfg(target_pointer_width = "64")]
#[lang = "isize"]
impl isize {
widening_impl! { isize, i128, 64 }
int_impl! { isize, i64, usize, 64, 63, -9223372036854775808, 9223372036854775807,
12, "0xaa00000000006e1", "0x6e10aa", "0x1234567890123456", "0x5634129078563412",
"0x6a2c48091e6a2c48", "[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
Expand All @@ -160,6 +240,7 @@ const ASCII_CASE_MASK: u8 = 0b0010_0000;

#[lang = "u8"]
impl u8 {
widening_impl! { u8, u16, 8 }
uint_impl! { u8, u8, 8, 255, 2, "0x82", "0xa", "0x12", "0x12", "0x48", "[0x12]",
"[0x12]", "", "" }

Expand Down Expand Up @@ -693,18 +774,21 @@ impl u8 {

#[lang = "u16"]
impl u16 {
widening_impl! { u16, u32, 16 }
uint_impl! { u16, u16, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
"[0x34, 0x12]", "[0x12, 0x34]", "", "" }
}

#[lang = "u32"]
impl u32 {
widening_impl! { u32, u64, 32 }
uint_impl! { u32, u32, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
"0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]", "[0x12, 0x34, 0x56, 0x78]", "", "" }
}

#[lang = "u64"]
impl u64 {
widening_impl! { u64, u128, 64 }
uint_impl! { u64, u64, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
"0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
"[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
Expand All @@ -727,13 +811,15 @@ impl u128 {
#[cfg(target_pointer_width = "16")]
#[lang = "usize"]
impl usize {
widening_impl! { usize, u32, 16 }
uint_impl! { usize, u16, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
"[0x34, 0x12]", "[0x12, 0x34]",
usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!() }
}
#[cfg(target_pointer_width = "32")]
#[lang = "usize"]
impl usize {
widening_impl! { usize, u64, 32 }
uint_impl! { usize, u32, 32, 4294967295, 8, "0x10000b3", "0xb301", "0x12345678",
"0x78563412", "0x1e6a2c48", "[0x78, 0x56, 0x34, 0x12]", "[0x12, 0x34, 0x56, 0x78]",
usize_isize_to_xe_bytes_doc!(), usize_isize_from_xe_bytes_doc!() }
Expand All @@ -742,6 +828,7 @@ impl usize {
#[cfg(target_pointer_width = "64")]
#[lang = "usize"]
impl usize {
widening_impl! { usize, u128, 64 }
uint_impl! { usize, u64, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
"0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
"[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
Expand Down
60 changes: 60 additions & 0 deletions library/core/src/num/uint_macros.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1378,6 +1378,36 @@ macro_rules! uint_impl {
(a as Self, b)
}

/// Calculates `self + rhs + carry` without the ability to overflow.
///
/// Performs "ternary addition" which takes in an extra bit to add, and may return an
/// additional bit of overflow. This allows for chaining together multiple additions
/// to create "big integers" which represent larger values.
///
/// # Examples
///
/// Basic usage
///
/// ```
/// #![feature(bigint_helper_methods)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".carrying_add(2, false), (7, false));")]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".carrying_add(2, true), (8, false));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, false), (0, true));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, true), (1, true));")]
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn carrying_add(self, rhs: Self, carry: bool) -> (Self, bool) {
// note: longer-term this should be done via an intrinsic, but this has been shown
// to generate optimal code for now, and LLVM doesn't have an equivalent intrinsic
let (a, b) = self.overflowing_add(rhs);
let (c, d) = a.overflowing_add(carry as $SelfT);
(c, b | d)
}

/// Calculates `self` - `rhs`
///
/// Returns a tuple of the subtraction along with a boolean indicating
Expand All @@ -1403,6 +1433,36 @@ macro_rules! uint_impl {
(a as Self, b)
}

/// Calculates `self - rhs - borrow` without the ability to overflow.
///
/// Performs "ternary subtraction" which takes in an extra bit to subtract, and may return
/// an additional bit of overflow. This allows for chaining together multiple subtractions
/// to create "big integers" which represent larger values.
///
/// # Examples
///
/// Basic usage
///
/// ```
/// #![feature(bigint_helper_methods)]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".borrowing_sub(2, false), (3, false));")]
#[doc = concat!("assert_eq!(5", stringify!($SelfT), ".borrowing_sub(2, true), (2, false));")]
#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".borrowing_sub(1, false), (", stringify!($SelfT), "::MAX, true));")]
#[doc = concat!("assert_eq!(0", stringify!($SelfT), ".borrowing_sub(1, true), (", stringify!($SelfT), "::MAX - 1, true));")]
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
#[must_use = "this returns the result of the operation, \
without modifying the original"]
#[inline]
pub const fn borrowing_sub(self, rhs: Self, borrow: bool) -> (Self, bool) {
// note: longer-term this should be done via an intrinsic, but this has been shown
// to generate optimal code for now, and LLVM doesn't have an equivalent intrinsic
let (a, b) = self.overflowing_sub(rhs);
let (c, d) = a.overflowing_sub(borrow as $SelfT);
(c, b | d)
}

/// Calculates the multiplication of `self` and `rhs`.
///
/// Returns a tuple of the multiplication along with a boolean
Expand Down

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