This is a separation of the DFA Unicode Decoder from
https://chromium-review.googlesource.com/c/v8/v8/+/789560
I attempted to make the DFA's table a bit more explicit in this CL. Still, the
linter prevents me from letting me present the array as a "table" in source
code. For a better representation, please refer to
https://docs.google.com/spreadsheets/d/1L9STtkmWs-A7HdK5ZmZ-wPZ_VBjQ3-Jj_xN9c6_hLKA
- - - - -
Now for a big copy-paste from 789560:
Essentially, reworks a standard FSM (imagine an
array of structs) and flattens it out into a single-dimension array.
Using Table 3-7 of the Unicode 10.0.0 standard (page 126 of
http://www.unicode.org/versions/Unicode10.0.0/ch03.pdf), we can nicely
map all bytes into one of 12 character classes:
00. 0x00-0x7F
01. 0x80-0x8F (split from general continuation because this range is not
valid after a 0xF0 leading byte)
02. 0x90-0x9F (split from general continuation because this range is not
valid after a 0xE0 nor a 0xF4 leading byte)
03. 0xA0-0xBF (the rest of the continuation range)
04. 0xC0-0xC1, 0xF5-0xFF (the joined range of invalid bytes, notice this
includes 255 which we use as a known bad byte during hex-to-int
decoding)
05. 0xC2-0xDF (leading bytes which require any continuation byte
afterwards)
06. 0xE0 (leading byte which requires a 0xA0-0xBF afterwards then any
continuation byte after that)
07. 0xE1-0xEC, 0xEE-0xEF (leading bytes which requires any continuation
afterwards then any continuation byte after that)
08. 0xED (leading byte which requires a 0x80-0x9F afterwards then any
continuation byte after that)
09. 0xF1-F3 (leading bytes which requires any continuation byte
afterwards then any continuation byte then any continuation byte)
10. 0xF0 (leading bytes which requires a 0x90-0xBF afterwards then any
continuation byte then any continuation byte)
11. 0xF4 (leading bytes which requires a 0x80-0x8F afterwards then any
continuation byte then any continuation byte)
Note that 0xF0 and 0xF1-0xF3 were swapped so that fewer bytes were
needed to represent the transition state ("9, 10, 10, 10" vs.
"10, 9, 9, 9").
Using these 12 classes as "transitions", we can map from one state to
the next. Each state is defined as some multiple of 12, so that we're
always starting at the 0th column of each row of the FSM. From each
state, we add the transition and get a index of the new row the FSM is
entering.
If at any point we encounter a bad byte, the state + bad-byte-transition
is guaranteed to map us into the first row of the FSM (which contains no
valid exiting transitions).
The key differences from Björn's original (or his self-modified) DFA is
the "bad" state is now mapped to 0 (or the first row of the FSM) instead
of 12 (the second row). This saves ~50 bytes when gzipping, and also
speeds up determining if a string is properly encoded (see his sample
code at http://bjoern.hoehrmann.de/utf-8/decoder/dfa/#performance).
Finally, I've replace his ternary check with an array access, to make
the algorithm branchless. This places a requirement on the caller to 0
out the code point between successful decodings, which it could always
have done because it's already branching.
R=marja@google.com
Bug:
Change-Id: I574f208a84dc5d06caba17127b0d41f7ce1a3395
Reviewed-on: https://chromium-review.googlesource.com/805357
Commit-Queue: Justin Ridgewell <jridgewell@google.com>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50012}
This patch normalizes the casing of hexadecimal digits in escape
sequences of the form `\xNN` and integer literals of the form
`0xNNNN`.
Previously, the V8 code base used an inconsistent mixture of uppercase
and lowercase.
Google’s C++ style guide uses uppercase in its examples:
https://google.github.io/styleguide/cppguide.html#Non-ASCII_Characters
Moreover, uppercase letters more clearly stand out from the lowercase
`x` (or `u`) characters at the start, as well as lowercase letters
elsewhere in strings.
BUG=v8:7109
TBR=marja@chromium.org,titzer@chromium.org,mtrofin@chromium.org,mstarzinger@chromium.org,rossberg@chromium.org,yangguo@chromium.org,mlippautz@chromium.org
NOPRESUBMIT=true
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I790e21c25d96ad5d95c8229724eb45d2aa9e22d6
Reviewed-on: https://chromium-review.googlesource.com/804294
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49810}
Verify that both UTF-8 decoders (incremental and non-incremental one) match the
expectations.
Also cleanup / harden the UTF-8 handling code, as suggested in
https://chromium-review.googlesource.com/c/v8/v8/+/671020/ .
BUG=chromium:765608
Change-Id: I6344d62ca15b75ac8e333421c94c4aa35ab8190d
Reviewed-on: https://chromium-review.googlesource.com/681217
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48229}
This code should not access bytes out of the permitted range in order to check
the range of a possible UTF-8 value. Instead, the length check should occur
before such checks.
BUG=chromium:667260, chromium:662822
Review-Url: https://codereview.chromium.org/2520053003
Cr-Commit-Position: refs/heads/master@{#41165}
