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read(io, Char): fix read with too many leading ones #50552

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merged 3 commits into from
Jul 17, 2023

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@StefanKarpinski StefanKarpinski commented Jul 14, 2023

Fixes #50532. The read(io, Char) method didn't correctly handle the case where the lead byte starts with too many leading ones; this fix makes it handle that case correctly, which makes read(io, Char) match collect(s) in its interpretation of what a character is in all invalid cases.

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Thanks! Now passes my tests from JuliaIO/BufferedStreams.jl#77 where I first noticed this issue.

@stevengj stevengj added io Involving the I/O subsystem: libuv, read, write, etc. strings "Strings!" bugfix This change fixes an existing bug labels Jul 14, 2023
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stevengj commented Jul 14, 2023

The following saves one comparison by utilizing UInt8 wraparound:

-    l::UInt8 = leading_ones(b0)
+    l = 0x08 * (0x04 - (leading_ones(b0) % UInt8))
     c = UInt32(b0) << 24
-    if 2 ≤ l ≤ 4
+    if l < 0x18
         s = 16
-        l = 8(4-l)

(Not sure if it's worth making s a UInt8 as well, since it's compared to l?)

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@StefanKarpinski
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I was kind of hoping the optimizer would figure that out for me, but might as well do it explicitly. This might be what I had intended the code to do originally but got foiled by promotion with Int.

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Maybe backport to 1.10 at least?

@stevengj stevengj added the backport 1.10 Change should be backported to the 1.10 release label Jul 14, 2023
@StefanKarpinski StefanKarpinski added the backport 1.6 Change should be backported to release-1.6 label Jul 17, 2023
@StefanKarpinski StefanKarpinski merged commit ffe1a07 into master Jul 17, 2023
@StefanKarpinski StefanKarpinski deleted the sk/fix-read-invalid-char branch July 17, 2023 14:16
KristofferC pushed a commit that referenced this pull request Jul 17, 2023
Fixes #50532. The `read(io, Char)` method didn't correctly handle the
case where the lead byte starts with too many leading ones; this fix
makes it handle that case correctly, which makes `read(io, Char)` match
`collect(s)` in its interpretation of what a character is in all invalid
cases. Also fix and test `read(::File, Char)` which has the same bug.

(cherry picked from commit ffe1a07)
KristofferC added a commit that referenced this pull request Jul 24, 2023
Backported PRs:
- [x] #50411 <!-- Fix weird dispatch of * with zero arguments -->
- [x] #50202 <!-- Remove dynamic dispatch from _wait/wait2 -->
- [x] #50064 <!-- Fix numbered prompt with input only with comment -->
- [x] #50026 <!-- Store heapsnapshot files in tempdir() instead of
current directory -->
- [x] #50402 <!-- Add CPU feature helper function -->
- [x] #50387 <!-- update newpages pointer after actually sweeping pages
-->
- [x] #50424 <!-- avoid potential type-instability in _replace_(str,
...) -->
- [x] #50444 <!-- Optimize getfield lowering to avoid boxing in some
cases -->
- [x] #50474 <!-- docs: Fix a `!!! note` which was miscapitalized -->
- [x] #50466 <!-- relax assertion involving pg->nold to reflect that it
may be a bit in… -->
- [x] #50490 <!-- Fix compat annotation for italic printstyled -->
- [x] #50488 <!-- fix typo in `Base.isassigned` with `Tridiagonal` -->
- [x] #50476 <!-- Profile: Add specifying dir for `take_heap_snapshot`
and handling if current dir is unwritable -->
- [x] #50461 <!-- fix typo in the --gcthreads argument description -->
- [x] #50528 <!-- ssair: Correctly handle stmt insertion at end of basic
block -->
- [x] #50533 <!-- ensure internal_obj_base_ptr checks whether objects
past freelist pointer are in freelist -->
- [x] #49322 <!-- improve cat design / performance -->
- [x] #50540 <!-- gc: remove over-eager assertion -->
- [x] #50542 <!-- gf: remove unnecessary assert cycle==depth -->
- [x] #50559 <!-- Expand kwcall lowering positional default check to
vararg -->
- [x] #50058 <!-- Add unwrapping mechanism for triangular mul and solves
-->
- [x] #50551 <!-- typeintersect: also record chained `innervars` -->
- [x] #50552 <!-- read(io, Char): fix read with too many leading ones
-->
- [x] #50541 <!-- precompile: ensure globals are not accidentally
created where disallowed -->
- [x] #50576 <!-- use atomic compare exchange when setting the GC
mark-bit -->
- [x] #50578 <!-- gf: make method overwrite/delete an error during
precompile -->
- [x] #50516 <!-- Fix visibility of assert on GCC12/13 -->
- [x] #50597 <!-- Fix memory corruption if task is launched inside
finalizer -->
- [x] #50591 <!-- build: fix various makefile bugs -->
- [x] #50599 <!-- faster invalid object lookup in conservative gc -->
- [x] #50634 <!-- 🤖 [master] Bump the SparseArrays stdlib from b4b0e72
to 99c99b4 -->
- [x] #50639 <!-- Backport LLVM patches to fix various issues. -->
- [x] #50546 <!-- Revert storage of method instance in LineInfoNode -->
- [x] #50631 <!-- Shift DCE pass to optimize imaging mode code better
-->
- [x] #50525 <!-- only check that values are finite in `generic_lufact`
when `check=true` -->
- [x] #50587 <!-- isassigned for ranges with BigInt indices -->
- [x] #50144 <!-- Page based heap size heuristics -->


Need manual backport:
- [ ] #50595 <!-- Rename ENV variable `JULIA_USE_NEW_PARSER` ->
`JULIA_USE_FLISP_PARSER` -->



Non-merged PRs with backport label:
- [ ] #50637 <!-- Remove SparseArrays legacy code -->
- [ ] #50618 <!-- inference: continue const-prop' when concrete-eval
returns non-inlineable -->
- [ ] #50598 <!-- only limit types in stack traces in the REPL -->
- [ ] #50594 <!-- Disallow non-index Integer types in isassigned -->
- [ ] #50568 <!-- `Array(::AbstractRange)` should return an `Array` -->
- [ ] #50523 <!-- Avoid generic call in most cases for getproperty -->
- [ ] #50172 <!-- print feature flags used for matching pkgimage -->
@KristofferC KristofferC removed the backport 1.10 Change should be backported to the 1.10 release label Jul 24, 2023
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read(io, Char) doesn't match collect(string) for malformed UTF-8
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