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tools/brotli: improve window size autodetect (#710)

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Window size is defined as:
    `(1 << BROTLI_PARAM_LGWIN) - 16`
in `c/include/brotli/encode.h`

Therefore we should probably take these 16 bytes into account.

Done basic manual testing:
$ python3 -c 'print ("A"*2046)' > t
$ bazel run -- //:brotli -w 0 -f -o $(realpath t).br $(realpath ./t)
$ python3 research/brotlidump.py t.br |& fgrep WSIZE
0000  c1                1000001 WSIZE   windowsize=(1<<12)-16=4080

New version properly detects window size of `4080`, while previous one used `2032`:
$ python3 research/brotlidump.py t.br |& fgrep WSIZE
0000  b1                0110001 WSIZE   windowsize=(1<<11)-16=2032
This commit is contained in:
Alexey Ivanov 2018-10-02 07:28:37 -07:00 committed by Eugene Kliuchnikov
parent 9402ac5c08
commit c94c6f805c
1 changed files with 2 additions and 3 deletions
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5
c/tools/brotli.c
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@ -943,10 +943,9 @@ static BROTLI_BOOL CompressFiles(Context* context) {
uint32_t lgwin = DEFAULT_LGWIN;
/* Use file size to limit lgwin. */
if (context->input_file_length >= 0) {
int32_t size = 1 << BROTLI_MIN_WINDOW_BITS;
lgwin = BROTLI_MIN_WINDOW_BITS;
while (size < context->input_file_length) {
size <<= 1;
while (BROTLI_MAX_BACKWARD_LIMIT(lgwin) <
(uint64_t)context->input_file_length) {
lgwin++;
if (lgwin == BROTLI_MAX_WINDOW_BITS) break;
}