crates/ryu/src/pretty/mod.rs

mod exponent;
mod mantissa;

use self::exponent::{write_exponent2, write_exponent3};
use self::mantissa::{write_mantissa, write_mantissa_long};
use crate::common;
use crate::d2s::{self, d2d, DOUBLE_EXPONENT_BITS, DOUBLE_MANTISSA_BITS};
use crate::f2s::{f2d, FLOAT_EXPONENT_BITS, FLOAT_MANTISSA_BITS};
use core::ptr;
#[cfg(feature = "no-panic")]
use no_panic::no_panic;

/// Print f64 to the given buffer and return number of bytes written.
///
/// At most 24 bytes will be written.
///
/// ## Special cases
///
/// This function **does not** check for NaN or infinity. If the input
/// number is not a finite float, the printed representation will be some
/// correctly formatted but unspecified numerical value.
///
/// Please check [`is_finite`] yourself before calling this function, or
/// check [`is_nan`] and [`is_infinite`] and handle those cases yourself.
///
/// [`is_finite`]: f64::is_finite
/// [`is_nan`]: f64::is_nan
/// [`is_infinite`]: f64::is_infinite
///
/// ## Safety
///
/// The `result` pointer argument must point to sufficiently many writable bytes
/// to hold Ryū's representation of `f`.
///
/// ## Example
///
/// ```
/// use std::{mem::MaybeUninit, slice, str};
///
/// let f = 1.234f64;
///
/// unsafe {
///     let mut buffer = [MaybeUninit::<u8>::uninit(); 24];
///     let len = ryu::raw::format64(f, buffer.as_mut_ptr() as *mut u8);
///     let slice = slice::from_raw_parts(buffer.as_ptr() as *const u8, len);
///     let print = str::from_utf8_unchecked(slice);
///     assert_eq!(print, "1.234");
/// }
/// ```
#[must_use]
#[cfg_attr(feature = "no-panic", no_panic)]
pub unsafe fn format64(f: f64, result: *mut u8) -> usize {
    let bits = f.to_bits();
    let sign = ((bits >> (DOUBLE_MANTISSA_BITS + DOUBLE_EXPONENT_BITS)) & 1) != 0;
    let ieee_mantissa = bits & ((1u64 << DOUBLE_MANTISSA_BITS) - 1);
    let ieee_exponent =
        (bits >> DOUBLE_MANTISSA_BITS) as u32 & ((1u32 << DOUBLE_EXPONENT_BITS) - 1);

    let mut index = 0isize;
    if sign {
        *result = b'-';
        index += 1;
    }

    if ieee_exponent == 0 && ieee_mantissa == 0 {
        ptr::copy_nonoverlapping(b"0.0".as_ptr(), result.offset(index), 3);
        return sign as usize + 3;
    }

    let v = d2d(ieee_mantissa, ieee_exponent);

    let length = d2s::decimal_length17(v.mantissa) as isize;
    let k = v.exponent as isize;
    let kk = length + k; // 10^(kk-1) <= v < 10^kk
    debug_assert!(k >= -324);

    if 0 <= k && kk <= 16 {
        // 1234e7 -> 12340000000.0
        write_mantissa_long(v.mantissa, result.offset(index + length));
        for i in length..kk {
            *result.offset(index + i) = b'0';
        }
        *result.offset(index + kk) = b'.';
        *result.offset(index + kk + 1) = b'0';
        index as usize + kk as usize + 2
    } else if 0 < kk && kk <= 16 {
        // 1234e-2 -> 12.34
        write_mantissa_long(v.mantissa, result.offset(index + length + 1));
        ptr::copy(result.offset(index + 1), result.offset(index), kk as usize);
        *result.offset(index + kk) = b'.';
        index as usize + length as usize + 1
    } else if -5 < kk && kk <= 0 {
        // 1234e-6 -> 0.001234
        *result.offset(index) = b'0';
        *result.offset(index + 1) = b'.';
        let offset = 2 - kk;
        for i in 2..offset {
            *result.offset(index + i) = b'0';
        }
        write_mantissa_long(v.mantissa, result.offset(index + length + offset));
        index as usize + length as usize + offset as usize
    } else if length == 1 {
        // 1e30
        *result.offset(index) = b'0' + v.mantissa as u8;
        *result.offset(index + 1) = b'e';
        index as usize + 2 + write_exponent3(kk - 1, result.offset(index + 2))
    } else {
        // 1234e30 -> 1.234e33
        write_mantissa_long(v.mantissa, result.offset(index + length + 1));
        *result.offset(index) = *result.offset(index + 1);
        *result.offset(index + 1) = b'.';
        *result.offset(index + length + 1) = b'e';
        index as usize
            + length as usize
            + 2
            + write_exponent3(kk - 1, result.offset(index + length + 2))
    }
}

/// Print f32 to the given buffer and return number of bytes written.
///
/// At most 16 bytes will be written.
///
/// ## Special cases
///
/// This function **does not** check for NaN or infinity. If the input
/// number is not a finite float, the printed representation will be some
/// correctly formatted but unspecified numerical value.
///
/// Please check [`is_finite`] yourself before calling this function, or
/// check [`is_nan`] and [`is_infinite`] and handle those cases yourself.
///
/// [`is_finite`]: f32::is_finite
/// [`is_nan`]: f32::is_nan
/// [`is_infinite`]: f32::is_infinite
///
/// ## Safety
///
/// The `result` pointer argument must point to sufficiently many writable bytes
/// to hold Ryū's representation of `f`.
///
/// ## Example
///
/// ```
/// use std::{mem::MaybeUninit, slice, str};
///
/// let f = 1.234f32;
///
/// unsafe {
///     let mut buffer = [MaybeUninit::<u8>::uninit(); 16];
///     let len = ryu::raw::format32(f, buffer.as_mut_ptr() as *mut u8);
///     let slice = slice::from_raw_parts(buffer.as_ptr() as *const u8, len);
///     let print = str::from_utf8_unchecked(slice);
///     assert_eq!(print, "1.234");
/// }
/// ```
#[must_use]
#[cfg_attr(feature = "no-panic", no_panic)]
pub unsafe fn format32(f: f32, result: *mut u8) -> usize {
    let bits = f.to_bits();
    let sign = ((bits >> (FLOAT_MANTISSA_BITS + FLOAT_EXPONENT_BITS)) & 1) != 0;
    let ieee_mantissa = bits & ((1u32 << FLOAT_MANTISSA_BITS) - 1);
    let ieee_exponent = (bits >> FLOAT_MANTISSA_BITS) & ((1u32 << FLOAT_EXPONENT_BITS) - 1);

    let mut index = 0isize;
    if sign {
        *result = b'-';
        index += 1;
    }

    if ieee_exponent == 0 && ieee_mantissa == 0 {
        ptr::copy_nonoverlapping(b"0.0".as_ptr(), result.offset(index), 3);
        return sign as usize + 3;
    }

    let v = f2d(ieee_mantissa, ieee_exponent);

    let length = common::decimal_length9(v.mantissa) as isize;
    let k = v.exponent as isize;
    let kk = length + k; // 10^(kk-1) <= v < 10^kk
    debug_assert!(k >= -45);

    if 0 <= k && kk <= 13 {
        // 1234e7 -> 12340000000.0
        write_mantissa(v.mantissa, result.offset(index + length));
        for i in length..kk {
            *result.offset(index + i) = b'0';
        }
        *result.offset(index + kk) = b'.';
        *result.offset(index + kk + 1) = b'0';
        index as usize + kk as usize + 2
    } else if 0 < kk && kk <= 13 {
        // 1234e-2 -> 12.34
        write_mantissa(v.mantissa, result.offset(index + length + 1));
        ptr::copy(result.offset(index + 1), result.offset(index), kk as usize);
        *result.offset(index + kk) = b'.';
        index as usize + length as usize + 1
    } else if -6 < kk && kk <= 0 {
        // 1234e-6 -> 0.001234
        *result.offset(index) = b'0';
        *result.offset(index + 1) = b'.';
        let offset = 2 - kk;
        for i in 2..offset {
            *result.offset(index + i) = b'0';
        }
        write_mantissa(v.mantissa, result.offset(index + length + offset));
        index as usize + length as usize + offset as usize
    } else if length == 1 {
        // 1e30
        *result.offset(index) = b'0' + v.mantissa as u8;
        *result.offset(index + 1) = b'e';
        index as usize + 2 + write_exponent2(kk - 1, result.offset(index + 2))
    } else {
        // 1234e30 -> 1.234e33
        write_mantissa(v.mantissa, result.offset(index + length + 1));
        *result.offset(index) = *result.offset(index + 1);
        *result.offset(index + 1) = b'.';
        *result.offset(index + length + 1) = b'e';
        index as usize
            + length as usize
            + 2
            + write_exponent2(kk - 1, result.offset(index + length + 2))
    }
}