fast32/src/base32/encode_bytes.rs at main · rogusdev/fast32 · GitHub

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// unsafe writing adapted from https://doc.rust-lang.org/src/alloc/vec/mod.rs.html#1878

use core::ptr::write;

use crate::shared::*;

use super::alphabet::{BITS, WIDTH_DEC, WIDTH_ENC};

const U8_MASK_MID_2: u8 = 0b01111100;

const U8_MASK_MID_1: u8 = 0b00111110;

/// Capacity needed in dest `Vec<u8>` to encode this byte array -- without padding!

///

/// Also see padded [`capacity_encode`](super::Alphabet32Padded::capacity_encode())

#[inline]

pub const fn capacity_encode(a: &[u8]) -> usize {

// https://stackoverflow.com/questions/23636240/how-do-i-predict-the-required-size-of-a-base32-decode-output

(a.len() * WIDTH_ENC + (WIDTH_DEC - 1)) / WIDTH_DEC

}

#[inline]

const fn rem_enc(rem: usize) -> usize {

match rem {

4 => 7,

3 => 5,

2 => 4,

1 => 2,

_ => 0,

}

/// Encode byte array with given encoding, into a `String`

///

/// Example:

/// ```

/// use fast32::base32::RFC4648;

/// assert_eq!(RFC4648.encode(&[0x00, 0x12]), "AAJA====");

/// ```

pub fn encode(enc: &'static [u8; BITS], a: &[u8]) -> String {

let len_dec = a.len();

let rem = len_dec % WIDTH_DEC;

let max = len_dec / WIDTH_DEC;

let p_max = max * WIDTH_ENC;

let rem_enc = rem_enc(rem);

let mut b = Vec::<u8>::with_capacity(p_max + rem_enc);

encode_inner(enc, a, &mut b, max, 0, p_max, rem, rem_enc);

unsafe { String::from_utf8_unchecked(b) }

}

/// Encode byte array with given encoding, into an existing `Vec<u8>`

///

/// Example:

/// ```

/// use fast32::base32::RFC4648;

/// let mut b = Vec::<u8>::with_capacity(8);

/// RFC4648.encode_into(&[0x00, 0x12], &mut b);

/// assert_eq!(&b, b"AAJA====");

/// ```

///

/// Panics if not enough capacity in `b` for encoding -- see [`capacity_encode`](self::capacity_encode())

pub fn encode_into(enc: &'static [u8; BITS], a: &[u8], b: &mut Vec<u8>) {

let len_dec = a.len();

let rem = len_dec % WIDTH_DEC;

let max = len_dec / WIDTH_DEC;

let len_enc = b.len();

let p_max = len_enc + max * WIDTH_ENC;

let rem_enc = rem_enc(rem);

assert!(

b.capacity() >= p_max + rem_enc,

"Missing capacity for encoding"

);

encode_inner(enc, a, b, max, len_enc, p_max, rem, rem_enc);

}

#[rustfmt::skip]

#[inline(always)]

fn encode_inner(enc: &'static [u8; BITS], a: &[u8], b: &mut Vec<u8>, max: usize, len_enc: usize, p_max: usize, rem: usize, rem_enc: usize) {

// 5 bytes is 8 chars exactly

// 4 bytes is 7 chars

// 3 bytes is 5 chars

// 2 bytes is 4 chars

// 1 bytes is 2 chars

// 6 bytes is 10 chars

// 7 bytes is 12 chars

// 8 bytes is 13 chars

// 9 bytes is 15 chars

// (src_size * 8 + 4) / 5

// (1 * 8 + 4) / 5 == 2

// (2 * 8 + 4) / 5 == 4

// (3 * 8 + 4) / 5 == 5

// (4 * 8 + 4) / 5 == 7

// (5 * 8 + 4) / 5 == 8

// (6 * 8 + 4) / 5 == 10

// (7 * 8 + 4) / 5 == 12

// (8 * 8 + 4) / 5 == 13

// (9 * 8 + 4) / 5 == 15

// (dst_size * 5) / 8

// (2 * 5) / 8 == 1

// (4 * 5) / 8 == 2

// (5 * 5) / 8 == 3

// (7 * 5) / 8 == 4

// (8 * 5) / 8 == 5

// (10 * 5) / 8 == 6

// (12 * 5) / 8 == 7

// (13 * 5) / 8 == 8

// (15 * 5) / 8 == 9

for i in 0..max {

// adapted from https://doc.rust-lang.org/src/alloc/vec/mod.rs.html#1878

unsafe {

let c = i * WIDTH_DEC;

let p = len_enc + i * WIDTH_ENC;

let end = b.as_mut_ptr().add(p);

write(end , enc[( (a[c ] & U8_MASK_TOP_5) >> 3 ) as usize]);

write(end.add(1), enc[(((a[c ] & U8_MASK_BOT_3) << 2) | ((a[c+1] & U8_MASK_TOP_2) >> 6)) as usize]);

write(end.add(2), enc[( (a[c+1] & U8_MASK_MID_1) >> 1 ) as usize]);

write(end.add(3), enc[(((a[c+1] & U8_MASK_BOT_1) << 4) | ((a[c+2] & U8_MASK_TOP_4) >> 4)) as usize]);

write(end.add(4), enc[(((a[c+2] & U8_MASK_BOT_4) << 1) | ((a[c+3] & U8_MASK_TOP_1) >> 7)) as usize]);

write(end.add(5), enc[( (a[c+3] & U8_MASK_MID_2) >> 2 ) as usize]);

write(end.add(6), enc[(((a[c+3] & U8_MASK_BOT_2) << 3) | ((a[c+4] & U8_MASK_TOP_3) >> 5)) as usize]);

write(end.add(7), enc[( a[c+4] & U8_MASK_BOT_5 ) as usize]);

b.set_len(p + WIDTH_ENC);

}

match rem {

4 => unsafe {

let c = max * WIDTH_DEC;

let end = b.as_mut_ptr().add(p_max);

write(end , enc[( (a[c ] & U8_MASK_TOP_5) >> 3 ) as usize]);

write(end.add(1), enc[(((a[c ] & U8_MASK_BOT_3) << 2) | ((a[c+1] & U8_MASK_TOP_2) >> 6)) as usize]);

write(end.add(2), enc[( (a[c+1] & U8_MASK_MID_1) >> 1 ) as usize]);

write(end.add(3), enc[(((a[c+1] & U8_MASK_BOT_1) << 4) | ((a[c+2] & U8_MASK_TOP_4) >> 4)) as usize]);

write(end.add(4), enc[(((a[c+2] & U8_MASK_BOT_4) << 1) | ((a[c+3] & U8_MASK_TOP_1) >> 7)) as usize]);

write(end.add(5), enc[( (a[c+3] & U8_MASK_MID_2) >> 2 ) as usize]);

write(end.add(6), enc[(((a[c+3] & U8_MASK_BOT_2) << 3) ) as usize]);

b.set_len(p_max + rem_enc);

}

3 => unsafe {

let c = max * WIDTH_DEC;

let end = b.as_mut_ptr().add(p_max);

write(end , enc[( (a[c ] & U8_MASK_TOP_5) >> 3 ) as usize]);

write(end.add(1), enc[(((a[c ] & U8_MASK_BOT_3) << 2) | ((a[c+1] & U8_MASK_TOP_2) >> 6)) as usize]);

write(end.add(2), enc[( (a[c+1] & U8_MASK_MID_1) >> 1 ) as usize]);

write(end.add(3), enc[(((a[c+1] & U8_MASK_BOT_1) << 4) | ((a[c+2] & U8_MASK_TOP_4) >> 4)) as usize]);

write(end.add(4), enc[(((a[c+2] & U8_MASK_BOT_4) << 1) ) as usize]);

b.set_len(p_max + rem_enc);

}

2 => unsafe {

let c = max * WIDTH_DEC;

let end = b.as_mut_ptr().add(p_max);

write(end , enc[( (a[c ] & U8_MASK_TOP_5) >> 3 ) as usize]);

write(end.add(1), enc[(((a[c ] & U8_MASK_BOT_3) << 2) | ((a[c+1] & U8_MASK_TOP_2) >> 6)) as usize]);

write(end.add(2), enc[( (a[c+1] & U8_MASK_MID_1) >> 1 ) as usize]);

write(end.add(3), enc[(((a[c+1] & U8_MASK_BOT_1) << 4) ) as usize]);

b.set_len(p_max + rem_enc);

}

1 => unsafe {

let c = max * WIDTH_DEC;

let end = b.as_mut_ptr().add(p_max);

write(end , enc[( (a[c ] & U8_MASK_TOP_5) >> 3 ) as usize]);

write(end.add(1), enc[(((a[c ] & U8_MASK_BOT_3) << 2) ) as usize]);

b.set_len(p_max + rem_enc);

}

_ => {}

}

fast32/src/base32/encode_bytes.rs at main · rogusdev/fast32 · GitHub

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