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compression/huffman: tighten bit_len checks (fix SUSE -O3 build)

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The struct write_context bit_len attribute is always between 0 and 31,
but if the next patches are applied without this, SUSE GCC -O3 will
worry thusly:

 ../../lib/compression/lzxpress_huffman.c: In function
  ‘lzxpress_huffman_compress’:
 ../../lib/compression/lzxpress_huffman.c:953:5: error: assuming signed
  overflow does not occur when simplifying conditional to constant
  [-Werror=strict-overflow]
   if (wc->bit_len > 16) {
         ^
         cc1: all warnings being treated as errors

Inspection tell us that the invariant holds. Nevertheless, we can
safely use an unsigned type and insist that over- or under- flow is
bad.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Jeremy Allison <jra@samba.org>
This commit is contained in:
Douglas Bagnall 2022-12-07 12:01:32 +13:00 committed by Jeremy Allison
parent e7489be7be
commit 27af27f901
1 changed files with 3 additions and 2 deletions
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5
lib/compression/lzxpress_huffman.c
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@ -928,7 +928,7 @@ struct write_context {
size_t head; /* where lengths go */
size_t next_code; /* where symbol stream goes */
size_t pending_next_code; /* will be next_code */
int bit_len;
unsigned bit_len;
uint32_t bits;
};
@ -953,7 +953,8 @@ static inline bool write_bits(struct write_context *wc,
if (wc->bit_len > 16) {
uint32_t w = wc->bits >> (wc->bit_len - 16);
wc->bit_len -= 16;
if (wc->next_code + 2 > wc->dest_len) {
if (wc->next_code + 2 > wc->dest_len ||
unlikely(wc->bit_len > 16)) {
return false;
}
wc->dest[wc->next_code] = w & 0xff;