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prcwidth=1 (and likewise prcheight=1) yields prc widthexpn=0 via jpc_floorlog2, which is accepted by the positive-value option check. For resolution levels above 0 the encoder then computes cbgwidthexpn = prcwidthexpn - 1 = -1, and the negative exponent makes the precinct/code-block geometry produce zero code blocks, ending in a reachable assertion in jpc_tagtree_create() (SIGABRT) or a negative shift exponent (UB). The decoder already rejects prcwidthexpn < 1 (jpc_dec.c); mirror that bound in cp_create() where the > 15 check already lives, so invalid options are rejected at option-parse time. Fixes jasper-software#422.
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Summary
Fixes #422 —
prcwidth=1(andprcheight=1) passes the encoder's positive-value option check, butjpc_floorlog2(1) = 0, soprcwidthexpn = 0. For every resolution level above 0 the encoder then computescbgwidthexpn = prcwidthexpn - 1 = -1, the negative exponent drives the code-block-group geometry to produce zero code blocks, andjpc_tagtree_create(0, ...)aborts onassert(numleafsh > 0 && numleafsv > 0)(SIGABRT; a negative shift exponent under UBSan).Fix
The decoder already rejects
prcwidthexpn < 1for every resolution level (jpc_dec.c:837). This adds the mirror bound incp_create(), right where the existing> 15checks live, so the invalid option is rejected at option-parse time with a proper error message.Testing
jasper --input in.pgm --output out.jpc --output-format jpc -O prcwidth=1→runtime error: shift exponent 4294967295 is too large(UBSan) / assertion abort (release)invalid precinct width→jpc_encode failed(graceful)prcwidth=4and default encoding still work normally