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Add more text and examples to carrying_{add|mul} #90556

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Nov 5, 2021
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Add more text and examples to carrying_{add|mul} #90556

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63 changes: 48 additions & 15 deletions library/core/src/num/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,13 @@ depending on the target pointer size.
}

macro_rules! widening_impl {
($SelfT:ty, $WideT:ty, $BITS:literal) => {
($SelfT:ty, $WideT:ty, $BITS:literal, unsigned) => {
widening_impl!($SelfT, $WideT, $BITS, "");
};
($SelfT:ty, $WideT:ty, $BITS:literal, signed) => {
widening_impl!($SelfT, $WideT, $BITS, "# //");
};
($SelfT:ty, $WideT:ty, $BITS:literal, $AdaptiveTestPrefix:literal) => {
/// Calculates the complete product `self * rhs` without the possibility to overflow.
///
/// This returns the low-order (wrapping) bits and the high-order (overflow) bits
Expand Down Expand Up @@ -148,6 +154,33 @@ macro_rules! widening_impl {
/// assert_eq!(5u32.carrying_mul(2, 10), (20, 0));
/// assert_eq!(1_000_000_000u32.carrying_mul(10, 0), (1410065408, 2));
/// assert_eq!(1_000_000_000u32.carrying_mul(10, 10), (1410065418, 2));
#[doc = concat!($AdaptiveTestPrefix, "assert_eq!(",
stringify!($SelfT), "::MAX.carrying_mul(", stringify!($SelfT), "::MAX, ", stringify!($SelfT), "::MAX), ",
"(0, ", stringify!($SelfT), "::MAX));"
)]
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$AdaptiveTestPrefix is a bit of a hack because this currently doesn't pass on signed types. It's unclear to me whether it should -- there's open questions about this method on signed types in things like #90493 -- so for now it's just skipped and hidden.

/// ```
///
/// If `carry` is zero, this is similar to [`overflowing_mul`](Self::overflowing_mul),
/// except that it gives the value of the overflow instead of just whether one happened:
///
/// ```
/// #![feature(bigint_helper_methods)]
/// let r = u8::carrying_mul(7, 13, 0);
/// assert_eq!((r.0, r.1 != 0), u8::overflowing_mul(7, 13));
/// let r = u8::carrying_mul(13, 42, 0);
/// assert_eq!((r.0, r.1 != 0), u8::overflowing_mul(13, 42));
/// ```
///
/// The value of the first field in the returned tuple matches what you'd get
/// by combining the [`wrapping_mul`](Self::wrapping_mul) and
/// [`wrapping_add`](Self::wrapping_add) methods:
///
/// ```
/// #![feature(bigint_helper_methods)]
/// assert_eq!(
/// 789_u16.carrying_mul(456, 123).0,
/// 789_u16.wrapping_mul(456).wrapping_add(123),
/// );
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "bigint_helper_methods", issue = "85532")]
Expand All @@ -168,29 +201,29 @@ macro_rules! widening_impl {

#[lang = "i8"]
impl i8 {
widening_impl! { i8, i16, 8 }
widening_impl! { i8, i16, 8, signed }
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 }
widening_impl! { i16, i32, 16, signed }
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 }
widening_impl! { i32, i64, 32, signed }
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 }
widening_impl! { i64, i128, 64, signed }
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 @@ -212,7 +245,7 @@ impl i128 {
#[cfg(target_pointer_width = "16")]
#[lang = "isize"]
impl isize {
widening_impl! { isize, i32, 16 }
widening_impl! { isize, i32, 16, signed }
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 @@ -221,7 +254,7 @@ impl isize {
#[cfg(target_pointer_width = "32")]
#[lang = "isize"]
impl isize {
widening_impl! { isize, i64, 32 }
widening_impl! { isize, i64, 32, signed }
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 @@ -231,7 +264,7 @@ impl isize {
#[cfg(target_pointer_width = "64")]
#[lang = "isize"]
impl isize {
widening_impl! { isize, i128, 64 }
widening_impl! { isize, i128, 64, signed }
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 @@ -244,7 +277,7 @@ const ASCII_CASE_MASK: u8 = 0b0010_0000;

#[lang = "u8"]
impl u8 {
widening_impl! { u8, u16, 8 }
widening_impl! { u8, u16, 8, unsigned }
uint_impl! { u8, u8, i8, 8, 255, 2, "0x82", "0xa", "0x12", "0x12", "0x48", "[0x12]",
"[0x12]", "", "" }

Expand Down Expand Up @@ -793,21 +826,21 @@ impl u8 {

#[lang = "u16"]
impl u16 {
widening_impl! { u16, u32, 16 }
widening_impl! { u16, u32, 16, unsigned }
uint_impl! { u16, u16, i16, 16, 65535, 4, "0xa003", "0x3a", "0x1234", "0x3412", "0x2c48",
"[0x34, 0x12]", "[0x12, 0x34]", "", "" }
}

#[lang = "u32"]
impl u32 {
widening_impl! { u32, u64, 32 }
widening_impl! { u32, u64, 32, unsigned }
uint_impl! { u32, u32, i32, 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 }
widening_impl! { u64, u128, 64, unsigned }
uint_impl! { u64, u64, i64, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
"0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
"[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
Expand All @@ -830,15 +863,15 @@ impl u128 {
#[cfg(target_pointer_width = "16")]
#[lang = "usize"]
impl usize {
widening_impl! { usize, u32, 16 }
widening_impl! { usize, u32, 16, unsigned }
uint_impl! { usize, u16, isize, 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 }
widening_impl! { usize, u64, 32, unsigned }
uint_impl! { usize, u32, isize, 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 @@ -847,7 +880,7 @@ impl usize {
#[cfg(target_pointer_width = "64")]
#[lang = "usize"]
impl usize {
widening_impl! { usize, u128, 64 }
widening_impl! { usize, u128, 64, unsigned }
uint_impl! { usize, u64, isize, 64, 18446744073709551615, 12, "0xaa00000000006e1", "0x6e10aa",
"0x1234567890123456", "0x5634129078563412", "0x6a2c48091e6a2c48",
"[0x56, 0x34, 0x12, 0x90, 0x78, 0x56, 0x34, 0x12]",
Expand Down
15 changes: 15 additions & 0 deletions library/core/src/num/uint_macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1504,6 +1504,8 @@ macro_rules! uint_impl {
/// additional bit of overflow. This allows for chaining together multiple additions
/// to create "big integers" which represent larger values.
///
#[doc = concat!("This can be thought of as a ", stringify!($BITS), "-bit \"full adder\", in the electronics sense.")]
///
/// # Examples
///
/// Basic usage
Expand All @@ -1513,7 +1515,20 @@ macro_rules! uint_impl {
#[doc = concat!("assert_eq!(5", stringify!($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!($SelfT), "::MAX.carrying_add(0, true), (0, true));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, true), (1, true));")]
#[doc = concat!("assert_eq!(",
stringify!($SelfT), "::MAX.carrying_add(", stringify!($SelfT), "::MAX, true), ",
"(", stringify!($SelfT), "::MAX, true));"
)]
/// ```
///
/// If `carry` is false, this method is equivalent to [`overflowing_add`](Self::overflowing_add):
///
/// ```
/// #![feature(bigint_helper_methods)]
#[doc = concat!("assert_eq!(5_", stringify!($SelfT), ".carrying_add(2, false), 5_", stringify!($SelfT), ".overflowing_add(2));")]
#[doc = concat!("assert_eq!(", stringify!($SelfT), "::MAX.carrying_add(1, false), ", stringify!($SelfT), "::MAX.overflowing_add(1));")]
/// ```
#[unstable(feature = "bigint_helper_methods", issue = "85532")]
#[rustc_const_unstable(feature = "const_bigint_helper_methods", issue = "85532")]
Expand Down