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fixed panic in zeroing pages for the happy case #213

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Merged
lemire merged 1 commit into from
Nov 16, 2025
Merged

fixed panic in zeroing pages for the happy case #213

lemire merged 1 commit into from
Nov 16, 2025
+4 −1

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@whisk whisk commented Nov 15, 2025

Problem

When doing the ShiftRight for n * wordSize bits (the happy case), idx may end to be equal to the length of set, leading to out of range runtime error when zeroing the pages, see example:

--- FAIL: TestShiftRightFull (0.00s)
panic: runtime error: index out of range [15] with length 15 [recovered, repanicked]

goroutine 187 [running]:
testing.tRunner.func1.2({0x10089a580, 0x14000266b10})
	/opt/homebrew/opt/go/libexec/src/testing/testing.go:1872 +0x190
testing.tRunner.func1()
	/opt/homebrew/opt/go/libexec/src/testing/testing.go:1875 +0x31c
panic({0x10089a580?, 0x14000266b10?})
	/opt/homebrew/opt/go/libexec/src/runtime/panic.go:783 +0x120
github.com/bits-and-blooms/bitset.(*BitSet).ShiftRight(0x140004125c0?, 0x3c1?)
	/Users/whisk/devel/github.com/whisk/bitset/bitset.go:1560 +0x234
github.com/bits-and-blooms/bitset.TestShiftRightFull.func1(...)
	/Users/whisk/devel/github.com/whisk/bitset/bitset_test.go:2461
github.com/bits-and-blooms/bitset.TestShiftRightFull(0x14000416c40)
	/Users/whisk/devel/github.com/whisk/bitset/bitset_test.go:2473 +0x124
testing.tRunner(0x14000416c40, 0x1008aecc0)
	/opt/homebrew/opt/go/libexec/src/testing/testing.go:1934 +0xc8
created by testing.(*T).Run in goroutine 1
	/opt/homebrew/opt/go/libexec/src/testing/testing.go:1997 +0x364
FAIL	github.com/bits-and-blooms/bitset	0.388s
FAIL

The added testcase fails without the fix.

Fix

Capped iteration to the length of set, no to idx.

Misc

I plan to add some fuzz tests later to help with spotting similar errors in future.

@whisk whisk force-pushed the fix/ShiftRight-pages-zeroing branch from d933b4e to f0f8af2 Compare November 15, 2025 20:57
@lemire lemire merged commit 8c1b8bc into bits-and-blooms:master Nov 16, 2025
29 checks passed
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2 participants

@whisk @lemire