float.rs.html -- source
Description: Source to the Rust file `library/core/src/fmt/float.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::fmt::{Debug, Display, Formatter, LowerExp, Result, UpperExp};
    use crate::mem::MaybeUninit;
    use crate::num::flt2dec;

    // Don't inline this so callers don't use the stack space this function
    // requires unless they have to.
    #[inline(never)]
    fn float_to_decimal_common_exact<T>(
        fmt: &mut Formatter<'_>,
        num: &T,
        sign: flt2dec::Sign,
        precision: usize,
    ) -> Result
    where
        T: flt2dec::DecodableFloat,
    {
        // SAFETY: Possible undefined behavior, see FIXME(#53491)
        unsafe {
            let mut buf = MaybeUninit::<[u8; 1024]>::uninit(); // enough for f32 and f64
            let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 4]>::uninit();
            // FIXME(#53491): This is calling `get_mut` on an uninitialized
            // `MaybeUninit` (here and elsewhere in this file). Revisit this once
            // we decided whether that is valid or not.
            // We can do this only because we are libstd and coupled to the compiler.
            // (FWIW, using `freeze` would not be enough; `flt2dec::Part` is an enum!)
            let formatted = flt2dec::to_exact_fixed_str(
                flt2dec::strategy::grisu::format_exact,
                *num,
                sign,
                precision,
                buf.get_mut(),
                parts.get_mut(),
            );
            fmt.pad_formatted_parts(&formatted)
        }
    }

    // Don't inline this so callers that call both this and the above won't wind
    // up using the combined stack space of both functions in some cases.
    #[inline(never)]
    fn float_to_decimal_common_shortest<T>(
        fmt: &mut Formatter<'_>,
        num: &T,
        sign: flt2dec::Sign,
        precision: usize,
    ) -> Result
    where
        T: flt2dec::DecodableFloat,
    {
        // SAFETY: Possible undefined behavior, see FIXME(#53491)
        unsafe {
            // enough for f32 and f64
            let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninit();
            let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 4]>::uninit();
            // FIXME(#53491)
            let formatted = flt2dec::to_shortest_str(
                flt2dec::strategy::grisu::format_shortest,
                *num,
                sign,
                precision,
                buf.get_mut(),
                parts.get_mut(),
            );
            fmt.pad_formatted_parts(&formatted)
        }
    }

    // Common code of floating point Debug and Display.
    fn float_to_decimal_common<T>(
        fmt: &mut Formatter<'_>,
        num: &T,
        negative_zero: bool,
        min_precision: usize,
    ) -> Result
    where
        T: flt2dec::DecodableFloat,
    {
        let force_sign = fmt.sign_plus();
        let sign = match (force_sign, negative_zero) {
            (false, false) => flt2dec::Sign::Minus,
            (false, true) => flt2dec::Sign::MinusRaw,
            (true, false) => flt2dec::Sign::MinusPlus,
            (true, true) => flt2dec::Sign::MinusPlusRaw,
        };

        if let Some(precision) = fmt.precision {
            float_to_decimal_common_exact(fmt, num, sign, precision)
        } else {
            float_to_decimal_common_shortest(fmt, num, sign, min_precision)
        }
    }

    // Don't inline this so callers don't use the stack space this function
    // requires unless they have to.
    #[inline(never)]
    fn float_to_exponential_common_exact<T>(
        fmt: &mut Formatter<'_>,
        num: &T,
        sign: flt2dec::Sign,
        precision: usize,
        upper: bool,
    ) -> Result
    where
        T: flt2dec::DecodableFloat,
    {
        // SAFETY: Possible undefined behavior, see FIXME(#53491)
        unsafe {
            let mut buf = MaybeUninit::<[u8; 1024]>::uninit(); // enough for f32 and f64
            let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 6]>::uninit();
            // FIXME(#53491)
            let formatted = flt2dec::to_exact_exp_str(
                flt2dec::strategy::grisu::format_exact,
                *num,
                sign,
                precision,
                upper,
                buf.get_mut(),
                parts.get_mut(),
            );
            fmt.pad_formatted_parts(&formatted)
        }
    }

    // Don't inline this so callers that call both this and the above won't wind
    // up using the combined stack space of both functions in some cases.
    #[inline(never)]
    fn float_to_exponential_common_shortest<T>(
        fmt: &mut Formatter<'_>,
        num: &T,
        sign: flt2dec::Sign,
        upper: bool,
    ) -> Result
    where
        T: flt2dec::DecodableFloat,
    {
        // SAFETY: Possible undefined behavior, see FIXME(#53491)
        unsafe {
            // enough for f32 and f64
            let mut buf = MaybeUninit::<[u8; flt2dec::MAX_SIG_DIGITS]>::uninit();
            let mut parts = MaybeUninit::<[flt2dec::Part<'_>; 6]>::uninit();
            // FIXME(#53491)
            let formatted = flt2dec::to_shortest_exp_str(
                flt2dec::strategy::grisu::format_shortest,
                *num,
                sign,
                (0, 0),
                upper,
                buf.get_mut(),
                parts.get_mut(),
            );
            fmt.pad_formatted_parts(&formatted)
        }
    }

    // Common code of floating point LowerExp and UpperExp.
    fn float_to_exponential_common<T>(fmt: &mut Formatter<'_>, num: &T, upper: bool) -> Result
    where
        T: flt2dec::DecodableFloat,
    {
        let force_sign = fmt.sign_plus();
        let sign = match force_sign {
            false => flt2dec::Sign::Minus,
            true => flt2dec::Sign::MinusPlus,
        };

        if let Some(precision) = fmt.precision {
            // 1 integral digit + `precision` fractional digits = `precision + 1` total digits
            float_to_exponential_common_exact(fmt, num, sign, precision + 1, upper)
        } else {
            float_to_exponential_common_shortest(fmt, num, sign, upper)
        }
    }

    macro_rules! floating {
        ($ty:ident) => {
            #[stable(feature = "rust1", since = "1.0.0")]
            impl Debug for $ty {
                fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                    float_to_decimal_common(fmt, self, true, 1)
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl Display for $ty {
                fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                    float_to_decimal_common(fmt, self, false, 0)
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl LowerExp for $ty {
                fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                    float_to_exponential_common(fmt, self, false)
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl UpperExp for $ty {
                fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                    float_to_exponential_common(fmt, self, true)
                }
            }
        };
    }

    floating! { f32 }
    floating! { f64 }