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Fix left shift on signed int channel setting sign bit and causing UB #28

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Merged
MarkCallow merged 2 commits into from
Jul 15, 2026
Merged

Fix left shift on signed int channel setting sign bit and causing UB #28

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47d346f
Fix left shift on signed int channel setting sign bit and causing UB
walcht Jul 13, 2026
01b51a8
Add comment on why `channel` is cast into uint32_t
walcht Jul 14, 2026
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8 changes: 7 additions & 1 deletion createdfd.c
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Original file line number Diff line number Diff line change
Expand Up @@ -117,10 +117,16 @@ static void writeSample(uint32_t *DFD, int sampleNo, int channel,
if (channel == 3) channel = KHR_DF_CHANNEL_RGBSDA_ALPHA;
channel = setChannelFlags(channel, suffix);

// `channel` is cast into an uint32_t to avoid the following issue:
// When `channel` is 192, the following UB occurs: 11000000 << 24
// Setting sign bit of an integer via a left shift operation is UB.
//
// TODO: This is the least intrusive solution for the moment. Ideally,
// writeSample should take uint32_t params.
sample[KHR_DF_SAMPLEWORD_BITOFFSET] =
(offset << KHR_DF_SAMPLESHIFT_BITOFFSET) |
((bits - 1) << KHR_DF_SAMPLESHIFT_BITLENGTH) |
(channel << KHR_DF_SAMPLESHIFT_CHANNELID);
((uint32_t)channel << KHR_DF_SAMPLESHIFT_CHANNELID);
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walcht marked this conversation as resolved.

sample[KHR_DF_SAMPLEWORD_SAMPLEPOSITION_ALL] = 0;

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