use crate::deflate::core::deflate_flags::{
TDEFL_FORCE_ALL_RAW_BLOCKS, TDEFL_GREEDY_PARSING_FLAG, TDEFL_RLE_MATCHES,
};
const DEFAULT_CM: u8 = 8;
const DEFAULT_CINFO: u8 = 7 << 4;
const _DEFAULT_FDICT: u8 = 0;
const DEFAULT_CMF: u8 = DEFAULT_CM | DEFAULT_CINFO;
// CMF used for RLE (technically it uses a window size of 0 but the lowest that can
// be specified in the header corresponds to a window size of 1 << (0 + 8) aka 256.
const MIN_CMF: u8 = DEFAULT_CM; // | 0
/// The 16-bit value consisting of CMF and FLG must be divisible by this to be valid.
const FCHECK_DIVISOR: u8 = 31;
/// Generate FCHECK from CMF and FLG (without FCKECH )so that they are correct according to the
/// specification, i.e (CMF*256 + FCHK) % 31 = 0.
/// Returns flg with the FCHKECK bits added (any existing FCHECK bits are ignored).
#[inline]
fn add_fcheck(cmf: u8, flg: u8) -> u8 {
let rem = ((usize::from(cmf) * 256) + usize::from(flg)) % usize::from(FCHECK_DIVISOR);
// Clear existing FCHECK if any
let flg = flg & 0b11100000;
// Casting is safe as rem can't overflow since it is a value mod 31
// We can simply add the value to flg as (31 - rem) will never be above 2^5
flg + (FCHECK_DIVISOR - rem as u8)
}
#[inline]
const fn zlib_level_from_flags(flags: u32) -> u8 {
use crate::deflate::core::NUM_PROBES;
let num_probes = flags & (super::MAX_PROBES_MASK as u32);
if (flags & TDEFL_GREEDY_PARSING_FLAG != 0) || (flags & TDEFL_RLE_MATCHES != 0) {
if num_probes <= 1 {
0
} else {
1
}
} else if num_probes >= NUM_PROBES[9] {
3
} else {
2
}
}
#[inline]
const fn cmf_from_flags(flags: u32) -> u8 {
if (flags & TDEFL_RLE_MATCHES == 0) && (flags & TDEFL_FORCE_ALL_RAW_BLOCKS == 0) {
DEFAULT_CMF
// If we are using RLE encoding or no compression the window bits can be set as the
// minimum.
} else {
MIN_CMF
}
}
/// Get the zlib header for the level using the default window size and no
/// dictionary.
#[inline]
fn header_from_level(level: u8, flags: u32) -> [u8; 2] {
let cmf = cmf_from_flags(flags);
[cmf, add_fcheck(cmf, level << 6)]
}
/// Create a zlib header from the given compression flags.
/// Only level is considered.
#[inline]
pub fn header_from_flags(flags: u32) -> [u8; 2] {
let level = zlib_level_from_flags(flags);
header_from_level(level, flags)
}
#[cfg(test)]
mod test {
use crate::shared::MZ_DEFAULT_WINDOW_BITS;
#[test]
fn zlib() {
use super::super::*;
use super::*;
let test_level = |level, expected| {
let flags = create_comp_flags_from_zip_params(
level,
MZ_DEFAULT_WINDOW_BITS,
CompressionStrategy::Default as i32,
);
assert_eq!(zlib_level_from_flags(flags), expected);
};
assert_eq!(zlib_level_from_flags(DEFAULT_FLAGS), 2);
test_level(0, 0);
test_level(1, 0);
test_level(2, 1);
test_level(3, 1);
for i in 4..=8 {
test_level(i, 2)
}
test_level(9, 3);
test_level(10, 3);
}
#[test]
fn test_header() {
let header = super::header_from_level(3, 0);
assert_eq!(
((usize::from(header[0]) * 256) + usize::from(header[1])) % 31,
0
);
}
}