Commit94bb6c4

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Fix overflow danger in SampleHeapTupleVisible(), take 2

28328ec addressed one overflow danger inSampleHeapTupleVisible() but introduced another, albeit a less likelyone. Modify the binary search code to remove this danger.Reported-by: Richard GuoReviewed-by: Richard Guo, Ranier VilelaDiscussion:https://postgr.es/m/CAMbWs4_bE%2BNscChbKWzw6HZOipCUyXfA5133qvoXQ654D3B2gQ%40mail.gmail.com

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Lines changed: 5 additions & 11 deletions

Original file line number	Diff line number	Diff line change
`@@ -2574,11 +2574,8 @@ SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,`
`2574`	`2574`
`2575`	`2575`	`if (scan->rs_flags&SO_ALLOW_PAGEMODE)`
`2576`	`2576`	`{`
`2577`		`-uint32start,`
`2578`		`-end;`
`2579`		`-`
`2580`		`-if (hscan->rs_ntuples==0)`
`2581`		`-return false;`
	`2577`	`+uint32start=0,`
	`2578`	`+end=hscan->rs_ntuples;`
`2582`	`2579`
`2583`	`2580`	`/*`
`2584`	`2581`	`* In pageatatime mode, heap_prepare_pagescan() already did visibility`
`@@ -2589,18 +2586,15 @@ SampleHeapTupleVisible(TableScanDesc scan, Buffer buffer,`
`2589`	`2586`	`* in increasing order, but it's not clear that there would be enough`
`2590`	`2587`	`* gain to justify the restriction.`
`2591`	`2588`	`*/`
`2592`		`-start=0;`
`2593`		`-end=hscan->rs_ntuples-1;`
`2594`		`-`
`2595`		`-while (start <=end)`
	`2589`	`+while (start<end)`
`2596`	`2590`	`{`
`2597`		`-uint32mid=(start+end) /2;`
	`2591`	`+uint32mid=start+(end-start) /2;`
`2598`	`2592`	`OffsetNumbercuroffset=hscan->rs_vistuples[mid];`
`2599`	`2593`
`2600`	`2594`	`if (tupoffset==curoffset)`
`2601`	`2595`	`return true;`
`2602`	`2596`	`elseif (tupoffset<curoffset)`
`2603`		`-end=mid-1;`
	`2597`	`+end=mid;`
`2604`	`2598`	`else`
`2605`	`2599`	`start=mid+1;`
`2606`	`2600`	`}`

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