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.
29 lines
1.1 KiB
Diff
29 lines
1.1 KiB
Diff
From 5dff5afab0c68d0d0c4385d72e6f0c030b613960 Mon Sep 17 00:00:00 2001
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From: patch <patch@local>
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Date: Mon, 18 May 2026 20:57:54 -0700
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Subject: [PATCH 1/2] Redirect pMCU to sMCUs[0] when iMCU < 0 (MCU_SKIP)
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---
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src/jpeg.inl | 5 ++++-
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1 file changed, 4 insertions(+), 1 deletion(-)
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diff --git a/src/jpeg.inl b/src/jpeg.inl
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index a60b548..26bcf6f 100644
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--- a/src/jpeg.inl
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+++ b/src/jpeg.inl
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@@ -1824,7 +1824,10 @@ static int JPEGDecodeMCU_P(JPEGIMAGE *pJPEG, int iMCU, int *iDCPredictor)
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unsigned short *pFast;
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uint32_t usHuff; // this prevents an unnecessary & 65535 for shorts
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signed int iPositive, iNegative, iCoeff;
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- signed short *pMCU = &pJPEG->sMCUs[iMCU & 0xffffff];
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+ // CrossPoint patch: redirect pMCU to sMCUs[0] when MCU_SKIP to avoid
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+ // a wild pointer (~33 MB past sMCUs) that store-faults on AC writes.
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+ signed short *pMCU = (iMCU < 0) ? pJPEG->sMCUs
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+ : &pJPEG->sMCUs[iMCU & 0xffffff];
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uint32_t ulBitOff;
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my_ulong ulCode, ulBits, ulTemp; // local copies to allow compiler to use register vars
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uint8_t *pBuf;
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--
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2.50.1 (Apple Git-155)
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