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Remove double bounds check #77

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merged 2 commits into from
Jan 14, 2025
Merged

Remove double bounds check #77

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100400b
fold explicit bounds checks into the logic
folkertdev Jan 14, 2025
e5f7314
simplify `match`
folkertdev Jan 14, 2025
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121 changes: 57 additions & 64 deletions libbz2-rs-sys/src/decompress.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -213,25 +213,24 @@
($s:expr) => {
if groupPos == 0 {
groupNo += 1;
if groupNo >= nSelectors as i32 {
error!(BZ_DATA_ERROR);
} else {
groupPos = 50;
gSel = $s.selector[groupNo as usize];
gLimit = gSel;
gPerm = gSel;
gBase = gSel;
gMinlen = $s.minLens[gSel as usize];
}
gSel = match $s.selector[..usize::from(nSelectors)].get(groupNo as usize) {
Some(&gSel) => gSel,
None => error!(BZ_DATA_ERROR),
};
gLimit = gSel;
gPerm = gSel;
gBase = gSel;
gMinlen = $s.minLens[gSel as usize];
groupPos = 50;
}
groupPos -= 1;
};
}

macro_rules! error {
($code:ident) => {
($code:ident) => {{
break 'save_state_and_return ReturnCode::$code;
};
}};
}

match s.state {
Expand Down Expand Up @@ -356,14 +355,11 @@

uc = GET_BYTE!(strm, s);

if uc == 0x17 {
// skips to `State::BZ_X_ENDHDR_2`
current_block = BZ_X_ENDHDR_2;
} else if uc != 0x31 {
error!(BZ_DATA_ERROR);
} else {
current_block = BZ_X_BLKHDR_2;
}
match uc {
0x17 => current_block = BZ_X_ENDHDR_2,
0x31 => current_block = BZ_X_BLKHDR_2,
_ => error!(BZ_DATA_ERROR),

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};
Comment on lines +358 to +362
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this is just a cleanup that i spotted

}
match current_block {
BZ_X_ENDHDR_2 => {
Expand Down Expand Up @@ -768,12 +764,11 @@
if zn > 20 {
error!(BZ_DATA_ERROR);
} else if zvec <= s.limit[gLimit as usize][zn as usize] {
if !(0..258).contains(&(zvec - s.base[gBase as usize][zn as usize])) {
error!(BZ_DATA_ERROR);
} else {
nextSym = s.perm[gPerm as usize]
[(zvec - s.base[gBase as usize][zn as usize]) as usize];
}
let index = zvec - s.base[gBase as usize][zn as usize];
nextSym = match s.perm[gPerm as usize].get(index as usize) {
Some(&nextSym) => nextSym,
None => error!(BZ_DATA_ERROR),

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};
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the s.perm[i] arrays are 258 elements long, so the check for the index value to be in bounds was happening twice (though of course llvm might optimize that out)

} else {
zn += 1;
current_block = BZ_X_MTF_6;
Expand All @@ -785,43 +780,42 @@
if zn > 20 {
error!(BZ_DATA_ERROR);
} else if zvec <= s.limit[gLimit as usize][zn as usize] {
if !(0..258).contains(&(zvec - s.base[gBase as usize][zn as usize])) {
error!(BZ_DATA_ERROR);
let index = zvec - s.base[gBase as usize][zn as usize];
nextSym = match s.perm[gPerm as usize].get(index as usize) {
Some(&nextSym) => nextSym,
None => error!(BZ_DATA_ERROR),

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};
if nextSym == BZ_RUNA as i32 || nextSym == BZ_RUNB as i32 {
current_block = Block46;
} else {
nextSym = s.perm[gPerm as usize]
[(zvec - s.base[gBase as usize][zn as usize]) as usize];
if nextSym == BZ_RUNA as i32 || nextSym == BZ_RUNB as i32 {
current_block = Block46;
} else {
es += 1;
uc = s.seqToUnseq[s.mtfa[s.mtfbase[0_usize] as usize] as usize];
s.unzftab[uc as usize] += es;
match s.smallDecompress {
DecompressMode::Small => {
while es > 0 {
if nblock >= 100000 * nblockMAX100k as u32 {
error!(BZ_DATA_ERROR);
} else {
ll16[nblock as usize] = uc as u16;
nblock += 1;
es -= 1;
}
es += 1;
uc = s.seqToUnseq[s.mtfa[s.mtfbase[0_usize] as usize] as usize];
s.unzftab[uc as usize] += es;
match s.smallDecompress {
DecompressMode::Small => {
while es > 0 {
if nblock >= 100000 * nblockMAX100k as u32 {
error!(BZ_DATA_ERROR);

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} else {
ll16[nblock as usize] = uc as u16;
nblock += 1;
es -= 1;
}
}
DecompressMode::Fast => {
while es > 0 {
if nblock >= 100000 * nblockMAX100k as u32 {
error!(BZ_DATA_ERROR);
} else {
tt[nblock as usize] = uc as u32;
nblock += 1;
es -= 1;
}
}
DecompressMode::Fast => {
while es > 0 {
if nblock >= 100000 * nblockMAX100k as u32 {
error!(BZ_DATA_ERROR);

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} else {
tt[nblock as usize] = uc as u32;
nblock += 1;
es -= 1;
}
}
}
current_block = Block40;
}
current_block = Block40;
}
} else {
zn += 1;
Expand All @@ -833,12 +827,11 @@
if zn > 20 {
error!(BZ_DATA_ERROR);
} else if zvec <= s.limit[gLimit as usize][zn as usize] {
if !(0..258).contains(&(zvec - s.base[gBase as usize][zn as usize])) {
error!(BZ_DATA_ERROR);
} else {
nextSym = s.perm[gPerm as usize]
[(zvec - s.base[gBase as usize][zn as usize]) as usize];
}
let index = zvec - s.base[gBase as usize][zn as usize];
nextSym = match s.perm[gPerm as usize].get(index as usize) {
Some(&nextSym) => nextSym,
None => error!(BZ_DATA_ERROR),

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};
} else {
zn += 1;
current_block = BZ_X_MTF_2;
Expand Down Expand Up @@ -1285,8 +1278,6 @@

EOB = s.nInUse + 1;
nblockMAX100k = s.blockSize100k as u8;
groupNo = -1;
groupPos = 0;
Comment on lines -1288 to -1289
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moved over to hopefully make it clearer why groupNo cannot be unsigned (currently anyway, maybe with some extra refactoring).

s.unzftab.fill(0);

/*-- MTF init --*/
Expand All @@ -1302,6 +1293,8 @@
/*-- end MTF init --*/

nblock = 0;
groupNo = -1;
groupPos = 0;
update_group_pos!(s);

zn = gMinlen;
Expand Down
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