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add read_bits_l

png-branch
an 2019-03-10 01:27:56 -05:00
parent 9bea0d895f
commit f5ceea654e
1 changed files with 76 additions and 26 deletions
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102
source/durandal/bit.rs
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@ -2,13 +2,14 @@
use crate::durandal::err::*;
/// Reads `width` bits from `b` starting at bit `cr_bit` into an integer.
/// Reads `width` bits from `b` starting at bit `cr_bit` into an integer, most
/// significant bit first.
///
/// # Errors
///
/// The function will return an error if `width` is 0 or more than 64, or if
/// `(cr_bit + width - 1) / 8` would overflow an index into `b`.
pub fn read_bits(b: &[u8], cr_bit: usize, width: u8) -> ResultS<(usize, u64)>
pub fn read_bits_b(b: &[u8], cr_bit: usize, width: u8) -> ResultS<(usize, u64)>
{
if width < 1 || width > 64 {
bail!("invalid number of bits");
@ -47,59 +48,108 @@ pub fn read_bits(b: &[u8], cr_bit: usize, width: u8) -> ResultS<(usize, u64)>
}
}
/// The same as `read_bits_b`, but least-significant bit first.
pub fn read_bits_l(b: &[u8], cr_bit: usize, width: u8) -> ResultS<(usize, u64)>
{
let (nx_bit, res) = read_bits_b(b, cr_bit, width)?;
Ok((nx_bit, reverse_bits(res) >> (64 - width)))
}
fn reverse_bits(v: u64) -> u64
{
// TODO: change this to u64::reverse_bits when stabilized
let v = v >> 1 & 0x5555_5555_5555_5555 | ((v & 0x5555_5555_5555_5555) << 1);
let v = v >> 2 & 0x3333_3333_3333_3333 | ((v & 0x3333_3333_3333_3333) << 2);
let v = v >> 4 & 0x0F0F_0F0F_0F0F_0F0F | ((v & 0x0F0F_0F0F_0F0F_0F0F) << 4);
v.swap_bytes()
}
fn get_bytes(b: &[u8], num_bytes: usize, f: usize) -> [u8; 8]
{
match num_bytes {
8 |
7 => [b[f], b[f+1], b[f+2], b[f+3], b[f+4], b[f+5], b[f+6], b[f+7]],
6 => [b[f], b[f+1], b[f+2], b[f+3], b[f+4], b[f+5], b[f+6], 0],
5 => [b[f], b[f+1], b[f+2], b[f+3], b[f+4], b[f+5], 0, 0],
4 => [b[f], b[f+1], b[f+2], b[f+3], b[f+4], 0, 0, 0],
3 => [b[f], b[f+1], b[f+2], b[f+3], 0, 0, 0, 0],
2 => [b[f], b[f+1], b[f+2], 0, 0, 0, 0, 0],
1 => [b[f], b[f+1], 0, 0, 0, 0, 0, 0],
0 => [b[f], 0, 0, 0, 0, 0, 0, 0],
_ => panic!("invalid number of bytes to read ({})", num_bytes),
6 => [b[f], b[f+1], b[f+2], b[f+3], b[f+4], b[f+5], b[f+6], 0 ],
5 => [b[f], b[f+1], b[f+2], b[f+3], b[f+4], b[f+5], 0, 0 ],
4 => [b[f], b[f+1], b[f+2], b[f+3], b[f+4], 0, 0, 0 ],
3 => [b[f], b[f+1], b[f+2], b[f+3], 0, 0, 0, 0 ],
2 => [b[f], b[f+1], b[f+2], 0, 0, 0, 0, 0 ],
1 => [b[f], b[f+1], 0, 0, 0, 0, 0, 0 ],
0 => [b[f], 0, 0, 0, 0, 0, 0, 0 ],
_ => {
panic!("invalid number of bytes to read ({})", num_bytes);
}
}
}
#[test]
fn bit_tests()
{
const INPUT: &[u8] = &[0b011_00101, 0b10101010, 0b00010000, 0b00000000,
0b11111111, 0b11100001, 0b10101100, 0b00110011,
const INPUT: &[u8] = &[0b011_00101, 0b10101010, 0b00010000, 0b00000000,
0b11111111, 0b11100001, 0b10101100, 0b00110011,
0b10_1001_01, 0b11100_000, 0b00000111, 0b000000_01,
0b11001010, 0b10101111, 0b00101011, 0b0_1101010,
0b11010101, 0b10100011, 0b01010101, 0b11_000001];
0b11001010, 0b10101111, 0b00101011, 0b0_1101010,
0b11010101, 0b10100011, 0b01010101, 0b11_000001];
let (p, n) = read_bits(INPUT, 0, 3).unwrap();
let (p, n) = read_bits_b(INPUT, 0, 3).unwrap();
assert_eq!(n, 0b011);
let (p, n) = read_bits(INPUT, p, 63).unwrap();
assert_eq!(n, 0x16A8_4003_FF86_B0CE);
let (p, n) = read_bits_b(INPUT, p, 63).unwrap();
assert_eq!(n, 0b001011010101000010000000000001111111111100001101011000011001110);
let (p, n) = read_bits(INPUT, p, 4).unwrap();
let (p, n) = read_bits_b(INPUT, p, 4).unwrap();
assert_eq!(n, 0b1001);
let (p, n) = read_bits(INPUT, p, 7).unwrap();
let (p, n) = read_bits_b(INPUT, p, 7).unwrap();
assert_eq!(n, 0b0111100);
let (p, n) = read_bits(INPUT, p, 17).unwrap();
let (p, n) = read_bits_b(INPUT, p, 17).unwrap();
assert_eq!(n, 0b00000000111000000);
let (p, n) = read_bits(INPUT, p, 27).unwrap();
let (p, n) = read_bits_b(INPUT, p, 27).unwrap();
assert_eq!(n, 0b011100101010101111001010110);
let (p, n) = read_bits(INPUT, p, 33).unwrap();
let (p, n) = read_bits_b(INPUT, p, 33).unwrap();
assert_eq!(n, 0b110101011010101101000110101010111);
let (p, n) = read_bits(INPUT, p, 6).unwrap();
assert_eq!(n, 1);
let (p, n) = read_bits_b(INPUT, p, 6).unwrap();
assert_eq!(n, 0b000001);
let e = read_bits(INPUT, p, 1);
let e = read_bits_b(INPUT, p, 1);
assert!(if let Err(_) = e {true} else {false});
let e = read_bits(INPUT, p, 2);
let e = read_bits_b(INPUT, p, 2);
assert!(if let Err(_) = e {true} else {false});
let (p, n) = read_bits_l(INPUT, 0, 3).unwrap();
assert_eq!(n, 0b110);
let (p, n) = read_bits_l(INPUT, p, 63).unwrap();
assert_eq!(n, 0b011100110000110101100001111111111100000000000010000101010110100);
let (p, n) = read_bits_l(INPUT, p, 4).unwrap();
assert_eq!(n, 0b1001);
let (p, n) = read_bits_l(INPUT, p, 7).unwrap();
assert_eq!(n, 0b0011110);
let (p, n) = read_bits_l(INPUT, p, 17).unwrap();
assert_eq!(n, 0b00000011100000000);
let (p, n) = read_bits_l(INPUT, p, 27).unwrap();
assert_eq!(n, 0b011010100111101010101001110);
let (p, n) = read_bits_l(INPUT, p, 33).unwrap();
assert_eq!(n, 0b111010101011000101101010110101011);
let (p, n) = read_bits_l(INPUT, p, 6).unwrap();
assert_eq!(n, 0b100000);
let e = read_bits_l(INPUT, p, 1);
assert!(if let Err(_) = e {true} else {false});
let e = read_bits_l(INPUT, p, 2);
assert!(if let Err(_) = e {true} else {false});
}