Function malachite_base::slices::slice_trailing_zeros

source · 
pub fn slice_trailing_zeros<T: Eq + Zero>(xs: &[T]) -> usize
Expand description

Counts the number of zeros that a slice ends with.

Worst-case complexity

$T(n) = O(n)$

$M(n) = O(1)$

where $T$ is time, $M$ is additional memory, and $n$ is xs.len().

Examples

use malachite_base::slices::slice_trailing_zeros;

assert_eq!(slice_trailing_zeros::<u32>(&[1, 2, 3]), 0);
assert_eq!(slice_trailing_zeros::<u32>(&[1, 2, 3, 0, 0, 0]), 3);
Examples found in repository?
src/num/conversion/string/to_sci.rs (line 138)
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fn fmt_sci_unsigned<T: PrimitiveUnsigned>(
    mut x: T,
    f: &mut Formatter,
    options: ToSciOptions,
) -> std::fmt::Result
where
    BaseFmtWrapper<T>: Display,
{
    match options.size_options {
        SciSizeOptions::Complete | SciSizeOptions::Scale(0) => write_helper(x, f, options),
        SciSizeOptions::Scale(scale) => {
            write_helper(x, f, options)?;
            if options.include_trailing_zeros {
                f.write_char('.')?;
                for _ in 0..scale {
                    f.write_char('0')?;
                }
            }
            Ok(())
        }
        SciSizeOptions::Precision(precision) => {
            let t_base = T::from(options.base);
            let log = if x == T::ZERO {
                0
            } else {
                x.floor_log_base(t_base)
            };
            if log < precision {
                // no exponent
                write_helper(x, f, options)?;
                if options.include_trailing_zeros {
                    let extra_zeros = precision - log - 1;
                    if extra_zeros != 0 {
                        f.write_char('.')?;
                        for _ in 0..extra_zeros {
                            f.write_char('0')?;
                        }
                    }
                }
                Ok(())
            } else {
                // exponent
                let mut e = log;
                let neg_scale = log - precision + 1;
                if let Some(base_log) = options.base.checked_log_base_2() {
                    x.shr_round_assign(base_log * neg_scale, options.rounding_mode);
                } else {
                    x.div_round_assign(Pow::pow(t_base, neg_scale), options.rounding_mode);
                }
                let mut chars = x.to_digits_desc(&options.base);
                let mut len = chars.len();
                let p = usize::exact_from(precision);
                if len > p {
                    // rounded up to a power of the base, need to reduce precision
                    chars.pop();
                    len -= 1;
                    e += 1;
                }
                assert_eq!(len, p);
                if !options.include_trailing_zeros {
                    chars.truncate(len - slice_trailing_zeros(&chars));
                }
                if options.lowercase {
                    for digit in &mut chars {
                        *digit = digit_to_display_byte_lower(*digit).unwrap();
                    }
                } else {
                    for digit in &mut chars {
                        *digit = digit_to_display_byte_upper(*digit).unwrap();
                    }
                }
                len = chars.len();
                if len != 1 {
                    chars.push(b'0');
                    chars.copy_within(1..len, 2);
                    chars[1] = b'.';
                }
                f.write_str(&String::from_utf8(chars).unwrap())?;
                write_exponent(f, options, e)
            }
        }
    }
}