Commitfd1444e

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pythongh-71810: Fix _PyLong_AsByteArray() undefined behavior (pythonGH-138873)

Don't read p[-1] when p is an empty string: when n==0.(cherry picked from commit8b5ce31)Co-authored-by: Victor Stinner <vstinner@python.org>

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Lines changed: 8 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -1046,8 +1046,14 @@ _PyLong_AsByteArray(PyLongObject* v,`
`1046`	`1046`	`just above didn't get to ensure there's a sign bit, and the`
`1047`	`1047`	`loop below wouldn't add one either. Make sure a sign bit`
`1048`	`1048`	`exists. */`
`1049`		`-unsignedcharmsb=*(p-pincr);`
`1050`		`-intsign_bit_set=msb >=0x80;`
	`1049`	`+intsign_bit_set;`
	`1050`	`+if (n>0) {`
	`1051`	`+unsignedcharmsb=*(p-pincr);`
	`1052`	`+sign_bit_set=msb >=0x80;`
	`1053`	`+ }`
	`1054`	`+else {`
	`1055`	`+sign_bit_set=0;`
	`1056`	`+ }`
`1051`	`1057`	`assert(accumbits==0);`
`1052`	`1058`	`if (sign_bit_set==do_twos_comp)`
`1053`	`1059`	`return0;`

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