src/libcore/fmt/num.rs - third_party/rust - Git at Google

 //! Integer and floating-point number formatting

 // ignore-tidy-undocumented-unsafe

 use crate::fmt;
 use crate::mem::MaybeUninit;
 use crate::num::flt2dec;
 use crate::ops::{Div, Rem, Sub};
 use crate::ptr;
 use crate::slice;
 use crate::str;

 #[doc(hidden)]
 trait Int:
     PartialEq + PartialOrd + Div<Output = Self> + Rem<Output = Self> + Sub<Output = Self> + Copy
 {
     fn zero() -> Self;
     fn from_u8(u: u8) -> Self;
     fn to_u8(&self) -> u8;
     fn to_u16(&self) -> u16;
     fn to_u32(&self) -> u32;
     fn to_u64(&self) -> u64;
     fn to_u128(&self) -> u128;
 }

 macro_rules! doit {
     ($($t:ident)*) => ($(impl Int for $t {
         fn zero() -> Self { 0 }
         fn from_u8(u: u8) -> Self { u as Self }
         fn to_u8(&self) -> u8 { *self as u8 }
         fn to_u16(&self) -> u16 { *self as u16 }
         fn to_u32(&self) -> u32 { *self as u32 }
         fn to_u64(&self) -> u64 { *self as u64 }
         fn to_u128(&self) -> u128 { *self as u128 }
     })*)
 }
 doit! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }

 /// A type that represents a specific radix
 #[doc(hidden)]
 trait GenericRadix {
     /// The number of digits.
     const BASE: u8;

     /// A radix-specific prefix string.
     const PREFIX: &'static str;

     /// Converts an integer to corresponding radix digit.
     fn digit(x: u8) -> u8;

     /// Format an integer using the radix using a formatter.
     fn fmt_int<T: Int>(&self, mut x: T, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // The radix can be as low as 2, so we need a buffer of at least 128
         // characters for a base 2 number.
         let zero = T::zero();
         let is_nonnegative = x >= zero;
         let mut buf = [MaybeUninit::<u8>::uninit(); 128];
         let mut curr = buf.len();
         let base = T::from_u8(Self::BASE);
         if is_nonnegative {
             // Accumulate each digit of the number from the least significant
             // to the most significant figure.
             for byte in buf.iter_mut().rev() {
                 let n = x % base; // Get the current place value.
                 x = x / base; // Deaccumulate the number.
                 byte.write(Self::digit(n.to_u8())); // Store the digit in the buffer.
                 curr -= 1;
                 if x == zero {
                     // No more digits left to accumulate.
                     break;
                 };
             }
         } else {
             // Do the same as above, but accounting for two's complement.
             for byte in buf.iter_mut().rev() {
                 let n = zero - (x % base); // Get the current place value.
                 x = x / base; // Deaccumulate the number.
                 byte.write(Self::digit(n.to_u8())); // Store the digit in the buffer.
                 curr -= 1;
                 if x == zero {
                     // No more digits left to accumulate.
                     break;
                 };
             }
         }
         let buf = &buf[curr..];
         let buf = unsafe {
             str::from_utf8_unchecked(slice::from_raw_parts(MaybeUninit::first_ptr(buf), buf.len()))
         };
         f.pad_integral(is_nonnegative, Self::PREFIX, buf)
     }
 }

 /// A binary (base 2) radix
 #[derive(Clone, PartialEq)]
 struct Binary;

 /// An octal (base 8) radix
 #[derive(Clone, PartialEq)]
 struct Octal;

 /// A hexadecimal (base 16) radix, formatted with lower-case characters
 #[derive(Clone, PartialEq)]
 struct LowerHex;

 /// A hexadecimal (base 16) radix, formatted with upper-case characters
 #[derive(Clone, PartialEq)]
 struct UpperHex;

 macro_rules! radix {
     ($T:ident, $base:expr, $prefix:expr, $($x:pat => $conv:expr),+) => {
         impl GenericRadix for $T {
             const BASE: u8 = $base;
             const PREFIX: &'static str = $prefix;
             fn digit(x: u8) -> u8 {
                 match x {
                     $($x => $conv,)+
                     x => panic!("number not in the range 0..={}: {}", Self::BASE - 1, x),
                 }
             }
         }
     }
 }

 radix! { Binary,    2, "0b", x @  0 ..=  1 => b'0' + x }
 radix! { Octal,     8, "0o", x @  0 ..=  7 => b'0' + x }
 radix! { LowerHex, 16, "0x", x @  0 ..=  9 => b'0' + x,
 x @ 10 ..= 15 => b'a' + (x - 10) }
 radix! { UpperHex, 16, "0x", x @  0 ..=  9 => b'0' + x,
 x @ 10 ..= 15 => b'A' + (x - 10) }

 macro_rules! int_base {
     ($Trait:ident for $T:ident as $U:ident -> $Radix:ident) => {
         #[stable(feature = "rust1", since = "1.0.0")]
         impl fmt::$Trait for $T {
             fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                 $Radix.fmt_int(*self as $U, f)
             }
         }
     };
 }

 macro_rules! debug {
     ($T:ident) => {
         #[stable(feature = "rust1", since = "1.0.0")]
         impl fmt::Debug for $T {
             #[inline]
             fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                 if f.debug_lower_hex() {
                     fmt::LowerHex::fmt(self, f)
                 } else if f.debug_upper_hex() {
                     fmt::UpperHex::fmt(self, f)
                 } else {
                     fmt::Display::fmt(self, f)
                 }
             }
         }
     };
 }

 macro_rules! integer {
     ($Int:ident, $Uint:ident) => {
         int_base! { Binary   for $Int as $Uint  -> Binary }
         int_base! { Octal    for $Int as $Uint  -> Octal }
         int_base! { LowerHex for $Int as $Uint  -> LowerHex }
         int_base! { UpperHex for $Int as $Uint  -> UpperHex }
         debug! { $Int }

         int_base! { Binary   for $Uint as $Uint -> Binary }
         int_base! { Octal    for $Uint as $Uint -> Octal }
         int_base! { LowerHex for $Uint as $Uint -> LowerHex }
         int_base! { UpperHex for $Uint as $Uint -> UpperHex }
         debug! { $Uint }
     };
 }
 integer! { isize, usize }
 integer! { i8, u8 }
 integer! { i16, u16 }
 integer! { i32, u32 }
 integer! { i64, u64 }
 integer! { i128, u128 }

 static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
       2021222324252627282930313233343536373839\
       4041424344454647484950515253545556575859\
       6061626364656667686970717273747576777879\
       8081828384858687888990919293949596979899";

 macro_rules! impl_Display {
     ($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
         fn $name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
             let mut buf = [MaybeUninit::<u8>::uninit(); 39];
             let mut curr = buf.len() as isize;
             let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
             let lut_ptr = DEC_DIGITS_LUT.as_ptr();

             unsafe {
                 // need at least 16 bits for the 4-characters-at-a-time to work.
                 assert!(crate::mem::size_of::<$u>() >= 2);

                 // eagerly decode 4 characters at a time
                 while n >= 10000 {
                     let rem = (n % 10000) as isize;
                     n /= 10000;

                     let d1 = (rem / 100) << 1;
                     let d2 = (rem % 100) << 1;
                     curr -= 4;
                     ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                     ptr::copy_nonoverlapping(lut_ptr.offset(d2), buf_ptr.offset(curr + 2), 2);
                 }

                 // if we reach here numbers are <= 9999, so at most 4 chars long
                 let mut n = n as isize; // possibly reduce 64bit math

                 // decode 2 more chars, if > 2 chars
                 if n >= 100 {
                     let d1 = (n % 100) << 1;
                     n /= 100;
                     curr -= 2;
                     ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                 }

                 // decode last 1 or 2 chars
                 if n < 10 {
                     curr -= 1;
                     *buf_ptr.offset(curr) = (n as u8) + b'0';
                 } else {
                     let d1 = n << 1;
                     curr -= 2;
                     ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                 }
             }

             let buf_slice = unsafe {
                 str::from_utf8_unchecked(
                     slice::from_raw_parts(buf_ptr.offset(curr), buf.len() - curr as usize))
             };
             f.pad_integral(is_nonnegative, "", buf_slice)
         }

         $(
             #[stable(feature = "rust1", since = "1.0.0")]
             impl fmt::Display for $t {
                 #[allow(unused_comparisons)]
                 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                     let is_nonnegative = *self >= 0;
                     let n = if is_nonnegative {
                         self.$conv_fn()
                     } else {
                         // convert the negative num to positive by summing 1 to it's 2 complement
                         (!self.$conv_fn()).wrapping_add(1)
                     };
                     $name(n, is_nonnegative, f)
                 }
             })*
     };
 }

 macro_rules! impl_Exp {
     ($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
         fn $name(
             mut n: $u,
             is_nonnegative: bool,
             upper: bool,
             f: &mut fmt::Formatter<'_>
         ) -> fmt::Result {
             let (mut n, mut exponent, trailing_zeros, added_precision) = {
                 let mut exponent = 0;
                 // count and remove trailing decimal zeroes
                 while n % 10 == 0 && n >= 10 {
                     n /= 10;
                     exponent += 1;
                 }
                 let trailing_zeros = exponent;

                 let (added_precision, subtracted_precision) = match f.precision() {
                     Some(fmt_prec) => {
                         // number of decimal digits minus 1
                         let mut tmp = n;
                         let mut prec = 0;
                         while tmp >= 10 {
                             tmp /= 10;
                             prec += 1;
                         }
                         (fmt_prec.saturating_sub(prec), prec.saturating_sub(fmt_prec))
                     }
                     None => (0,0)
                 };
                 for _ in 1..subtracted_precision {
                     n/=10;
                     exponent += 1;
                 }
                 if subtracted_precision != 0 {
                     let rem = n % 10;
                     n /= 10;
                     exponent += 1;
                     // round up last digit
                     if rem >= 5 {
                         n += 1;
                     }
                 }
                 (n, exponent, trailing_zeros, added_precision)
             };

             // 39 digits (worst case u128) + . = 40
             let mut buf = [MaybeUninit::<u8>::uninit(); 40];
             let mut curr = buf.len() as isize; //index for buf
             let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
             let lut_ptr = DEC_DIGITS_LUT.as_ptr();

             // decode 2 chars at a time
             while n >= 100 {
                 let d1 = ((n % 100) as isize) << 1;
                 curr -= 2;
                 unsafe {
                     ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                 }
                 n /= 100;
                 exponent += 2;
             }
             // n is <= 99, so at most 2 chars long
             let mut n = n as isize; // possibly reduce 64bit math
             // decode second-to-last character
             if n >= 10 {
                 curr -= 1;
                 unsafe {
                     *buf_ptr.offset(curr) = (n as u8 % 10_u8) + b'0';
                 }
                 n /= 10;
                 exponent += 1;
             }
             // add decimal point iff >1 mantissa digit will be printed
             if exponent != trailing_zeros || added_precision != 0 {
                 curr -= 1;
                 unsafe {
                     *buf_ptr.offset(curr) = b'.';
                 }
             }

             let buf_slice = unsafe {
                 // decode last character
                 curr -= 1;
                 *buf_ptr.offset(curr) = (n as u8) + b'0';

                 let len = buf.len() - curr as usize;
                 slice::from_raw_parts(buf_ptr.offset(curr), len)
             };

             // stores 'e' (or 'E') and the up to 2-digit exponent
             let mut exp_buf = [MaybeUninit::<u8>::uninit(); 3];
             let exp_ptr = MaybeUninit::first_ptr_mut(&mut exp_buf);
             let exp_slice = unsafe {
                 *exp_ptr.offset(0) = if upper {b'E'} else {b'e'};
                 let len = if exponent < 10 {
                     *exp_ptr.offset(1) = (exponent as u8) + b'0';
                     2
                 } else {
                     let off = exponent << 1;
                     ptr::copy_nonoverlapping(lut_ptr.offset(off), exp_ptr.offset(1), 2);
                     3
                 };
                 slice::from_raw_parts(exp_ptr, len)
             };

             let parts = &[
                 flt2dec::Part::Copy(buf_slice),
                 flt2dec::Part::Zero(added_precision),
                 flt2dec::Part::Copy(exp_slice)
             ];
             let sign = if !is_nonnegative {
                 "-"
             } else if f.sign_plus() {
                 "+"
             } else {
                 ""
             };
             let formatted = flt2dec::Formatted{sign, parts};
             f.pad_formatted_parts(&formatted)
         }

         $(
             #[stable(feature = "integer_exp_format", since = "1.42.0")]
             impl fmt::LowerExp for $t {
                 #[allow(unused_comparisons)]
                 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                     let is_nonnegative = *self >= 0;
                     let n = if is_nonnegative {
                         self.$conv_fn()
                     } else {
                         // convert the negative num to positive by summing 1 to it's 2 complement
                         (!self.$conv_fn()).wrapping_add(1)
                     };
                     $name(n, is_nonnegative, false, f)
                 }
             })*
         $(
             #[stable(feature = "integer_exp_format", since = "1.42.0")]
             impl fmt::UpperExp for $t {
                 #[allow(unused_comparisons)]
                 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                     let is_nonnegative = *self >= 0;
                     let n = if is_nonnegative {
                         self.$conv_fn()
                     } else {
                         // convert the negative num to positive by summing 1 to it's 2 complement
                         (!self.$conv_fn()).wrapping_add(1)
                     };
                     $name(n, is_nonnegative, true, f)
                 }
             })*
     };
 }

 // Include wasm32 in here since it doesn't reflect the native pointer size, and
 // often cares strongly about getting a smaller code size.
 #[cfg(any(target_pointer_width = "64", target_arch = "wasm32"))]
 mod imp {
     use super::*;
     impl_Display!(
         i8, u8, i16, u16, i32, u32, i64, u64, usize, isize
             as u64 via to_u64 named fmt_u64
     );
     impl_Exp!(
         i8, u8, i16, u16, i32, u32, i64, u64, usize, isize
             as u64 via to_u64 named exp_u64
     );
 }

 #[cfg(not(any(target_pointer_width = "64", target_arch = "wasm32")))]
 mod imp {
     use super::*;
     impl_Display!(i8, u8, i16, u16, i32, u32, isize, usize as u32 via to_u32 named fmt_u32);
     impl_Display!(i64, u64 as u64 via to_u64 named fmt_u64);
     impl_Exp!(i8, u8, i16, u16, i32, u32, isize, usize as u32 via to_u32 named exp_u32);
     impl_Exp!(i64, u64 as u64 via to_u64 named exp_u64);
 }

 impl_Display!(i128, u128 as u128 via to_u128 named fmt_u128);
 impl_Exp!(i128, u128 as u128 via to_u128 named exp_u128);
	//! Integer and floating-point number formatting

	// ignore-tidy-undocumented-unsafe

	use crate::fmt;
	use crate::mem::MaybeUninit;
	use crate::num::flt2dec;
	use crate::ops::{Div, Rem, Sub};
	use crate::ptr;
	use crate::slice;
	use crate::str;

	#[doc(hidden)]
	trait Int:
	PartialEq + PartialOrd + Div<Output = Self> + Rem<Output = Self> + Sub<Output = Self> + Copy
	{
	fn zero() -> Self;
	fn from_u8(u: u8) -> Self;
	fn to_u8(&self) -> u8;
	fn to_u16(&self) -> u16;
	fn to_u32(&self) -> u32;
	fn to_u64(&self) -> u64;
	fn to_u128(&self) -> u128;
	}

	macro_rules! doit {
	($($t:ident)*) => ($(impl Int for $t {
	fn zero() -> Self { 0 }
	fn from_u8(u: u8) -> Self { u as Self }
	fn to_u8(&self) -> u8 { *self as u8 }
	fn to_u16(&self) -> u16 { *self as u16 }
	fn to_u32(&self) -> u32 { *self as u32 }
	fn to_u64(&self) -> u64 { *self as u64 }
	fn to_u128(&self) -> u128 { *self as u128 }
	})*)
	}
	doit! { i8 i16 i32 i64 i128 isize u8 u16 u32 u64 u128 usize }

	/// A type that represents a specific radix
	#[doc(hidden)]
	trait GenericRadix {
	/// The number of digits.
	const BASE: u8;

	/// A radix-specific prefix string.
	const PREFIX: &'static str;

	/// Converts an integer to corresponding radix digit.
	fn digit(x: u8) -> u8;

	/// Format an integer using the radix using a formatter.
	fn fmt_int<T: Int>(&self, mut x: T, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	// The radix can be as low as 2, so we need a buffer of at least 128
	// characters for a base 2 number.
	let zero = T::zero();
	let is_nonnegative = x >= zero;
	let mut buf = [MaybeUninit::<u8>::uninit(); 128];
	let mut curr = buf.len();
	let base = T::from_u8(Self::BASE);
	if is_nonnegative {
	// Accumulate each digit of the number from the least significant
	// to the most significant figure.
	for byte in buf.iter_mut().rev() {
	let n = x % base; // Get the current place value.
	x = x / base; // Deaccumulate the number.
	byte.write(Self::digit(n.to_u8())); // Store the digit in the buffer.
	curr -= 1;
	if x == zero {
	// No more digits left to accumulate.
	break;
	};
	}
	} else {
	// Do the same as above, but accounting for two's complement.
	for byte in buf.iter_mut().rev() {
	let n = zero - (x % base); // Get the current place value.
	x = x / base; // Deaccumulate the number.
	byte.write(Self::digit(n.to_u8())); // Store the digit in the buffer.
	curr -= 1;
	if x == zero {
	// No more digits left to accumulate.
	break;
	};
	}
	}
	let buf = &buf[curr..];
	let buf = unsafe {
	str::from_utf8_unchecked(slice::from_raw_parts(MaybeUninit::first_ptr(buf), buf.len()))
	};
	f.pad_integral(is_nonnegative, Self::PREFIX, buf)
	}
	}

	/// A binary (base 2) radix
	#[derive(Clone, PartialEq)]
	struct Binary;

	/// An octal (base 8) radix
	#[derive(Clone, PartialEq)]
	struct Octal;

	/// A hexadecimal (base 16) radix, formatted with lower-case characters
	#[derive(Clone, PartialEq)]
	struct LowerHex;

	/// A hexadecimal (base 16) radix, formatted with upper-case characters
	#[derive(Clone, PartialEq)]
	struct UpperHex;

	macro_rules! radix {
	($T:ident, $base:expr, $prefix:expr, $($x:pat => $conv:expr),+) => {
	impl GenericRadix for $T {
	const BASE: u8 = $base;
	const PREFIX: &'static str = $prefix;
	fn digit(x: u8) -> u8 {
	match x {
	$($x => $conv,)+
	x => panic!("number not in the range 0..={}: {}", Self::BASE - 1, x),
	}
	}
	}
	}
	}

	radix! { Binary, 2, "0b", x @ 0 ..= 1 => b'0' + x }
	radix! { Octal, 8, "0o", x @ 0 ..= 7 => b'0' + x }
	radix! { LowerHex, 16, "0x", x @ 0 ..= 9 => b'0' + x,
	x @ 10 ..= 15 => b'a' + (x - 10) }
	radix! { UpperHex, 16, "0x", x @ 0 ..= 9 => b'0' + x,
	x @ 10 ..= 15 => b'A' + (x - 10) }

	macro_rules! int_base {
	($Trait:ident for $T:ident as $U:ident -> $Radix:ident) => {
	#[stable(feature = "rust1", since = "1.0.0")]
	impl fmt::$Trait for $T {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	$Radix.fmt_int(*self as $U, f)
	}
	}
	};
	}

	macro_rules! debug {
	($T:ident) => {
	#[stable(feature = "rust1", since = "1.0.0")]
	impl fmt::Debug for $T {
	#[inline]
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	if f.debug_lower_hex() {
	fmt::LowerHex::fmt(self, f)
	} else if f.debug_upper_hex() {
	fmt::UpperHex::fmt(self, f)
	} else {
	fmt::Display::fmt(self, f)
	}
	}
	}
	};
	}

	macro_rules! integer {
	($Int:ident, $Uint:ident) => {
	int_base! { Binary for $Int as $Uint -> Binary }
	int_base! { Octal for $Int as $Uint -> Octal }
	int_base! { LowerHex for $Int as $Uint -> LowerHex }
	int_base! { UpperHex for $Int as $Uint -> UpperHex }
	debug! { $Int }

	int_base! { Binary for $Uint as $Uint -> Binary }
	int_base! { Octal for $Uint as $Uint -> Octal }
	int_base! { LowerHex for $Uint as $Uint -> LowerHex }
	int_base! { UpperHex for $Uint as $Uint -> UpperHex }
	debug! { $Uint }
	};
	}
	integer! { isize, usize }
	integer! { i8, u8 }
	integer! { i16, u16 }
	integer! { i32, u32 }
	integer! { i64, u64 }
	integer! { i128, u128 }

	static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
	2021222324252627282930313233343536373839\
	4041424344454647484950515253545556575859\
	6061626364656667686970717273747576777879\
	8081828384858687888990919293949596979899";

	macro_rules! impl_Display {
	($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
	fn $name(mut n: $u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	let mut buf = [MaybeUninit::<u8>::uninit(); 39];
	let mut curr = buf.len() as isize;
	let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
	let lut_ptr = DEC_DIGITS_LUT.as_ptr();

	unsafe {
	// need at least 16 bits for the 4-characters-at-a-time to work.
	assert!(crate::mem::size_of::<$u>() >= 2);

	// eagerly decode 4 characters at a time
	while n >= 10000 {
	let rem = (n % 10000) as isize;
	n /= 10000;

	let d1 = (rem / 100) << 1;
	let d2 = (rem % 100) << 1;
	curr -= 4;
	ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
	ptr::copy_nonoverlapping(lut_ptr.offset(d2), buf_ptr.offset(curr + 2), 2);
	}

	// if we reach here numbers are <= 9999, so at most 4 chars long
	let mut n = n as isize; // possibly reduce 64bit math

	// decode 2 more chars, if > 2 chars
	if n >= 100 {
	let d1 = (n % 100) << 1;
	n /= 100;
	curr -= 2;
	ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
	}

	// decode last 1 or 2 chars
	if n < 10 {
	curr -= 1;
	*buf_ptr.offset(curr) = (n as u8) + b'0';
	} else {
	let d1 = n << 1;
	curr -= 2;
	ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
	}
	}

	let buf_slice = unsafe {
	str::from_utf8_unchecked(
	slice::from_raw_parts(buf_ptr.offset(curr), buf.len() - curr as usize))
	};
	f.pad_integral(is_nonnegative, "", buf_slice)
	}

	$(
	#[stable(feature = "rust1", since = "1.0.0")]
	impl fmt::Display for $t {
	#[allow(unused_comparisons)]
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	let is_nonnegative = *self >= 0;
	let n = if is_nonnegative {
	self.$conv_fn()
	} else {
	// convert the negative num to positive by summing 1 to it's 2 complement
	(!self.$conv_fn()).wrapping_add(1)
	};
	$name(n, is_nonnegative, f)
	}
	})*
	};
	}

	macro_rules! impl_Exp {
	($($t:ident),* as $u:ident via $conv_fn:ident named $name:ident) => {
	fn $name(
	mut n: $u,
	is_nonnegative: bool,
	upper: bool,
	f: &mut fmt::Formatter<'_>
	) -> fmt::Result {
	let (mut n, mut exponent, trailing_zeros, added_precision) = {
	let mut exponent = 0;
	// count and remove trailing decimal zeroes
	while n % 10 == 0 && n >= 10 {
	n /= 10;
	exponent += 1;
	}
	let trailing_zeros = exponent;

	let (added_precision, subtracted_precision) = match f.precision() {
	Some(fmt_prec) => {
	// number of decimal digits minus 1
	let mut tmp = n;
	let mut prec = 0;
	while tmp >= 10 {
	tmp /= 10;
	prec += 1;
	}
	(fmt_prec.saturating_sub(prec), prec.saturating_sub(fmt_prec))
	}
	None => (0,0)
	};
	for _ in 1..subtracted_precision {
	n/=10;
	exponent += 1;
	}
	if subtracted_precision != 0 {
	let rem = n % 10;
	n /= 10;
	exponent += 1;
	// round up last digit
	if rem >= 5 {
	n += 1;
	}
	}
	(n, exponent, trailing_zeros, added_precision)
	};

	// 39 digits (worst case u128) + . = 40
	let mut buf = [MaybeUninit::<u8>::uninit(); 40];
	let mut curr = buf.len() as isize; //index for buf
	let buf_ptr = MaybeUninit::first_ptr_mut(&mut buf);
	let lut_ptr = DEC_DIGITS_LUT.as_ptr();

	// decode 2 chars at a time
	while n >= 100 {
	let d1 = ((n % 100) as isize) << 1;
	curr -= 2;
	unsafe {
	ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
	}
	n /= 100;
	exponent += 2;
	}
	// n is <= 99, so at most 2 chars long
	let mut n = n as isize; // possibly reduce 64bit math
	// decode second-to-last character
	if n >= 10 {
	curr -= 1;
	unsafe {
	*buf_ptr.offset(curr) = (n as u8 % 10_u8) + b'0';
	}
	n /= 10;
	exponent += 1;
	}
	// add decimal point iff >1 mantissa digit will be printed
	if exponent != trailing_zeros \|\| added_precision != 0 {
	curr -= 1;
	unsafe {
	*buf_ptr.offset(curr) = b'.';
	}
	}

	let buf_slice = unsafe {
	// decode last character
	curr -= 1;
	*buf_ptr.offset(curr) = (n as u8) + b'0';

	let len = buf.len() - curr as usize;
	slice::from_raw_parts(buf_ptr.offset(curr), len)
	};

	// stores 'e' (or 'E') and the up to 2-digit exponent
	let mut exp_buf = [MaybeUninit::<u8>::uninit(); 3];
	let exp_ptr = MaybeUninit::first_ptr_mut(&mut exp_buf);
	let exp_slice = unsafe {
	*exp_ptr.offset(0) = if upper {b'E'} else {b'e'};
	let len = if exponent < 10 {
	*exp_ptr.offset(1) = (exponent as u8) + b'0';
	2
	} else {
	let off = exponent << 1;
	ptr::copy_nonoverlapping(lut_ptr.offset(off), exp_ptr.offset(1), 2);
	3
	};
	slice::from_raw_parts(exp_ptr, len)
	};

	let parts = &[
	flt2dec::Part::Copy(buf_slice),
	flt2dec::Part::Zero(added_precision),
	flt2dec::Part::Copy(exp_slice)
	];
	let sign = if !is_nonnegative {
	"-"
	} else if f.sign_plus() {
	"+"
	} else {
	""
	};
	let formatted = flt2dec::Formatted{sign, parts};
	f.pad_formatted_parts(&formatted)
	}

	$(
	#[stable(feature = "integer_exp_format", since = "1.42.0")]
	impl fmt::LowerExp for $t {
	#[allow(unused_comparisons)]
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	let is_nonnegative = *self >= 0;
	let n = if is_nonnegative {
	self.$conv_fn()
	} else {
	// convert the negative num to positive by summing 1 to it's 2 complement
	(!self.$conv_fn()).wrapping_add(1)
	};
	$name(n, is_nonnegative, false, f)
	}
	})*
	$(
	#[stable(feature = "integer_exp_format", since = "1.42.0")]
	impl fmt::UpperExp for $t {
	#[allow(unused_comparisons)]
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	let is_nonnegative = *self >= 0;
	let n = if is_nonnegative {
	self.$conv_fn()
	} else {
	// convert the negative num to positive by summing 1 to it's 2 complement
	(!self.$conv_fn()).wrapping_add(1)
	};
	$name(n, is_nonnegative, true, f)
	}
	})*
	};
	}

	// Include wasm32 in here since it doesn't reflect the native pointer size, and
	// often cares strongly about getting a smaller code size.
	#[cfg(any(target_pointer_width = "64", target_arch = "wasm32"))]
	mod imp {
	use super::*;
	impl_Display!(
	i8, u8, i16, u16, i32, u32, i64, u64, usize, isize
	as u64 via to_u64 named fmt_u64
	);
	impl_Exp!(
	i8, u8, i16, u16, i32, u32, i64, u64, usize, isize
	as u64 via to_u64 named exp_u64
	);
	}

	#[cfg(not(any(target_pointer_width = "64", target_arch = "wasm32")))]
	mod imp {
	use super::*;
	impl_Display!(i8, u8, i16, u16, i32, u32, isize, usize as u32 via to_u32 named fmt_u32);
	impl_Display!(i64, u64 as u64 via to_u64 named fmt_u64);
	impl_Exp!(i8, u8, i16, u16, i32, u32, isize, usize as u32 via to_u32 named exp_u32);
	impl_Exp!(i64, u64 as u64 via to_u64 named exp_u64);
	}

	impl_Display!(i128, u128 as u128 via to_u128 named fmt_u128);
	impl_Exp!(i128, u128 as u128 via to_u128 named exp_u128);