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fix(deflate): split some code into new module and fix panic in pad_to…
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,112 @@ | ||
| 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 | ||
| ); | ||
| } | ||
| } |