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//! Generic array are commonly used as a return value for hash digests, so
//! it's a good idea to allow to hexlify them easily. This module implements
//! `std::fmt::LowerHex` and `std::fmt::UpperHex` traits.
//!
//! Example:
//!
//! ```rust
//! # #[macro_use]
//! # extern crate generic_array;
//! # extern crate typenum;
//! # fn main() {
//! let array = arr![u8; 10, 20, 30];
//! assert_eq!(format!("{:x}", array), "0a141e");
//! # }
//! ```
//!

use {ArrayLength, GenericArray};
use core::fmt;
use core::ops::Add;
use core::str;
use typenum::*;

static LOWER_CHARS: &'static [u8] = b"0123456789abcdef";
static UPPER_CHARS: &'static [u8] = b"0123456789ABCDEF";


impl<T: ArrayLength<u8>> fmt::LowerHex for GenericArray<u8, T>
    where T: Add<T>,
          <T as Add<T>>::Output: ArrayLength<u8>
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let max_digits = f.precision().unwrap_or(self.len());
        if T::to_usize() < 1024 {
            // For small arrays use a stack allocated
            // buffer of 2x number of bytes
            let mut res = GenericArray::<u8, Sum<T, T>>::default();
            for (i, c) in self.iter().take(max_digits).enumerate() {
                res[i * 2] = LOWER_CHARS[(c >> 4) as usize];
                res[i * 2 + 1] = LOWER_CHARS[(c & 0xF) as usize];
            }
            f.write_str(unsafe { str::from_utf8_unchecked(&res[..max_digits * 2]) })?;
        } else {
            // For large array use chunks of up to 1024 bytes (2048 hex chars)
            let mut buf = [0u8; 2048];
            for chunk in self[..max_digits].chunks(1024) {
                for (i, c) in chunk.iter().enumerate() {
                    buf[i * 2] = LOWER_CHARS[(c >> 4) as usize];
                    buf[i * 2 + 1] = LOWER_CHARS[(c & 0xF) as usize];
                }
                f.write_str(unsafe { str::from_utf8_unchecked(&buf[..chunk.len() * 2]) })?;
            }
        }
        Ok(())
    }
}

impl<T: ArrayLength<u8>> fmt::UpperHex for GenericArray<u8, T>
    where T: Add<T>,
          <T as Add<T>>::Output: ArrayLength<u8>
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let max_digits = f.precision().unwrap_or(self.len());
        if T::to_usize() < 1024 {
            // For small arrays use a stack allocated
            // buffer of 2x number of bytes
            let mut res = GenericArray::<u8, Sum<T, T>>::default();
            for (i, c) in self.iter().take(max_digits).enumerate() {
                res[i * 2] = UPPER_CHARS[(c >> 4) as usize];
                res[i * 2 + 1] = UPPER_CHARS[(c & 0xF) as usize];
            }
            f.write_str(unsafe { str::from_utf8_unchecked(&res[..max_digits * 2]) })?;
        } else {
            // For large array use chunks of up to 1024 bytes (2048 hex chars)
            let mut buf = [0u8; 2048];
            for chunk in self[..max_digits].chunks(1024) {
                for (i, c) in chunk.iter().enumerate() {
                    buf[i * 2] = UPPER_CHARS[(c >> 4) as usize];
                    buf[i * 2 + 1] = UPPER_CHARS[(c & 0xF) as usize];
                }
                f.write_str(unsafe { str::from_utf8_unchecked(&buf[..chunk.len() * 2]) })?;
            }
        }
        Ok(())
    }
}