Jeremy Klein
9e68ced046
The previous patch_jpegdec.py used in-place string replacement with a single shared marker for two distinct DC writes (main store and successive-approximation update). If only one of the two anchors matched, the file was written half-patched and the shared marker locked the partial state in for every subsequent run. Generate the fixes as `git format-patch` artifacts under scripts/jpegdec_patches/, then apply them in lexical order via `git apply`. Idempotency is decided by git itself: `--check --reverse` succeeds means already applied; `--check` succeeds means appliable; neither aborts the build rather than leaving a half-patched file. No behaviour change to the patched JPEGDEC source: same redirect, same DC guards, same intent. Just stops the pre-build script from doing something it has no business doing.
42 lines
1.7 KiB
Diff
42 lines
1.7 KiB
Diff
From f6238b54c2de34c8e29b0d371a7e902d9cf579bf Mon Sep 17 00:00:00 2001
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From: patch <patch@local>
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Date: Mon, 18 May 2026 20:58:22 -0700
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Subject: [PATCH 2/2] Guard pMCU[0] DC writes against MCU_SKIP
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---
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src/jpeg.inl | 11 +++++++++--
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1 file changed, 9 insertions(+), 2 deletions(-)
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diff --git a/src/jpeg.inl b/src/jpeg.inl
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index 26bcf6f..1bd38b2 100644
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--- a/src/jpeg.inl
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+++ b/src/jpeg.inl
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@@ -1855,7 +1855,11 @@ static int JPEGDecodeMCU_P(JPEGIMAGE *pJPEG, int iMCU, int *iDCPredictor)
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{
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// (*iDCPredictor) |= iPositive; // in case the scan is run more than once
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// pMCU[0] = *iDCPredictor; // store in MCU[0]
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- pMCU[0] |= iPositive;
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+ // CrossPoint patch: guard against MCU_SKIP. The pMCU
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+ // redirect makes &sMCUs[0] safe to dereference, but
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+ // writing here would clobber the just-decoded Y DC.
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+ if (iMCU >= 0)
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+ pMCU[0] |= iPositive;
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}
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goto mcu_done; // that's it
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}
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@@ -1887,7 +1891,10 @@ static int JPEGDecodeMCU_P(JPEGIMAGE *pJPEG, int iMCU, int *iDCPredictor)
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ulCode <<= pJPEG->cApproxBitsLow; // successive approximation shift value
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(*iDCPredictor) += ulCode;
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}
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- pMCU[0] = (short)*iDCPredictor; // store in MCU[0]
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+ // CrossPoint patch: guard against MCU_SKIP. See note on the
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+ // matching SA write above.
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+ if (iMCU >= 0)
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+ pMCU[0] = (short)*iDCPredictor; // store in MCU[0]
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}
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// Now get the other 63 AC coefficients
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pFast = &pJPEG->usHuffAC[pJPEG->ucACTable * HUFF11SIZE];
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--
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2.50.1 (Apple Git-155)
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