deflate64/
input_buffer.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
use crate::InternalErr;
use std::cmp::min;

#[derive(Copy, Clone, Debug)]
pub(crate) struct BitsBuffer {
    bit_buffer: u32,
    bits_in_buffer: i32,
}

impl BitsBuffer {
    pub(crate) fn new() -> BitsBuffer {
        Self {
            bit_buffer: 0,
            bits_in_buffer: 0,
        }
    }
}

pub(crate) struct InputBuffer<'a> {
    pub bits: BitsBuffer,
    pub buffer: &'a [u8],
    pub read_bytes: usize,
}

impl<'a> InputBuffer<'a> {
    pub fn new(bits: BitsBuffer, buffer: &'a [u8]) -> Self {
        Self {
            bits,
            buffer,
            read_bytes: 0,
        }
    }

    pub fn available_bits(&self) -> i32 {
        self.bits.bits_in_buffer
    }

    pub fn available_bytes(&self) -> usize {
        self.buffer.len() + (self.bits.bits_in_buffer / 4) as usize
    }

    pub fn ensure_bits_available(&mut self, count: i32) -> bool {
        debug_assert!(0 < count && count <= 16, "count is invalid.");

        // manual inlining to improve perf
        if self.bits.bits_in_buffer < count {
            if self.needs_input() {
                return false;
            }

            // insert a byte to bitbuffer
            self.bits.bit_buffer |= (self.buffer[0] as u32) << self.bits.bits_in_buffer;
            self.advance(1);
            self.bits.bits_in_buffer += 8;

            if self.bits.bits_in_buffer < count {
                if self.needs_input() {
                    return false;
                }
                // insert a byte to bitbuffer
                self.bits.bit_buffer |= (self.buffer[0] as u32) << self.bits.bits_in_buffer;
                self.advance(1);
                self.bits.bits_in_buffer += 8;
            }
        }

        true
    }

    pub fn try_load_16bits(&mut self) -> u32 {
        if self.bits.bits_in_buffer < 8 {
            if self.buffer.len() > 1 {
                self.bits.bit_buffer |= (self.buffer[0] as u32) << self.bits.bits_in_buffer;
                self.bits.bit_buffer |= (self.buffer[1] as u32) << (self.bits.bits_in_buffer + 8);
                self.advance(2);
                self.bits.bits_in_buffer += 16;
            } else if !self.buffer.is_empty() {
                self.bits.bit_buffer |= (self.buffer[0] as u32) << self.bits.bits_in_buffer;
                self.advance(1);
                self.bits.bits_in_buffer += 8;
            }
        } else if self.bits.bits_in_buffer < 16 && !self.buffer.is_empty() {
            self.bits.bit_buffer |= (self.buffer[0] as u32) << self.bits.bits_in_buffer;
            self.advance(1);
            self.bits.bits_in_buffer += 8;
        }

        self.bits.bit_buffer
    }

    fn get_bit_mask(&self, count: i32) -> u32 {
        (1 << count) - 1
    }

    pub fn get_bits(&mut self, count: i32) -> Result<u16, InternalErr> {
        debug_assert!(0 < count && count <= 16, "count is invalid.");

        if !self.ensure_bits_available(count) {
            return Err(InternalErr::DataNeeded);
        }

        let result = (self.bits.bit_buffer & self.get_bit_mask(count)) as u16;
        self.bits.bit_buffer >>= count;
        self.bits.bits_in_buffer -= count;
        Ok(result)
    }

    pub fn copy_to(&mut self, mut output: &mut [u8]) -> usize {
        debug_assert!(self.bits.bits_in_buffer % 8 == 0);

        // Copy the bytes in bitBuffer first.
        let mut bytes_from_bit_buffer = 0;
        while self.bits.bits_in_buffer > 0 && !output.is_empty() {
            output[0] = self.bits.bit_buffer as u8;
            output = &mut output[1..];
            self.bits.bit_buffer >>= 8;
            self.bits.bits_in_buffer -= 8;
            bytes_from_bit_buffer += 1;
        }

        if output.is_empty() {
            return bytes_from_bit_buffer;
        }

        let length = min(output.len(), self.buffer.len());
        output[..length].copy_from_slice(&self.buffer[..length]);
        self.advance(length);
        bytes_from_bit_buffer + length
    }

    pub fn needs_input(&self) -> bool {
        self.buffer.is_empty()
    }

    /// <summary>Skip n bits in the buffer.</summary>
    pub fn skip_bits(&mut self, n: i32) {
        debug_assert!(
            self.bits.bits_in_buffer >= n,
            "No enough bits in the buffer, Did you call ensure_bits_available?"
        );
        self.bits.bit_buffer >>= n;
        self.bits.bits_in_buffer -= n;
    }

    /// <summary>Skips to the next byte boundary.</summary>
    pub fn skip_to_byte_boundary(&mut self) {
        self.bits.bit_buffer >>= self.bits.bits_in_buffer % 8;
        self.bits.bits_in_buffer -= self.bits.bits_in_buffer % 8;
    }

    fn advance(&mut self, buf: usize) {
        self.buffer = &self.buffer[buf..];
        self.read_bytes += buf;
    }
}