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Fix rem bigint operand dispatch on 32-bit #2381

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Fix rem bigint operand dispatch on 32-bit #2381

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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
- Fixed a bug where negative or oversized segment sizes were not rejected in binary matching
- Fixed the `network` mdns configuration to read the documented `host` key; the previously
required, undocumented `hostname` key is still accepted
- Fixed `rem` returning wrong results on 32-bit builds when an operand is a big integer with
a 64-bit magnitude, such as `(1 bsl 63) rem 7`

## [0.7.0-alpha.1] - 2026-04-06

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5 changes: 2 additions & 3 deletions src/libAtomVM/bif.c
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Expand Up @@ -1443,7 +1443,7 @@ static term rem_boxed_helper(Context *ctx, uint32_t fail_label, uint32_t live, t
RAISE_ERROR_BIF(fail_label, BADARITH_ATOM);
}
if (term_is_boxed_integer(arg2)) {
size |= term_boxed_size(arg2);
size = MAX(size, (int) term_boxed_size(arg2));
} else if (UNLIKELY(!term_is_integer(arg2))) {
TRACE("error: arg1: 0x%lx, arg2: 0x%lx\n", arg1, arg2);
RAISE_ERROR_BIF(fail_label, BADARITH_ATOM);
Expand All @@ -1466,8 +1466,7 @@ static term rem_boxed_helper(Context *ctx, uint32_t fail_label, uint32_t live, t
}

#if BOXED_TERMS_REQUIRED_FOR_INT64 == 2
case 2:
case 3: {
case 2: {
avm_int64_t val1 = term_maybe_unbox_int64(arg1);
avm_int64_t val2 = term_maybe_unbox_int64(arg2);
if (UNLIKELY(val2 == 0)) {
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19 changes: 19 additions & 0 deletions tests/erlang_tests/bigint.erl
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Expand Up @@ -259,8 +259,27 @@ test_rem() ->
),
<<"E3AE0EA63AE33EA79B071316BC9A7F1B">> = erlang:integer_to_binary(Int8 rem Int9, 16),

% operands with a 64-bit magnitude take 3 boxed terms on 32-bit builds and
% must not be mistaken for regular 2-term boxed int64 values
Int10 = erlang:binary_to_integer(?MODULE:id(<<"8000000000000000">>), 16),
Int11 = erlang:binary_to_integer(?MODULE:id(<<"8000000000000005">>), 16),
Int12 = erlang:binary_to_integer(?MODULE:id(<<"-8000000000000001">>), 16),
Int13 = erlang:binary_to_integer(?MODULE:id(<<"FFFFFFFFFFFFFFFF">>), 16),
Int14 = erlang:binary_to_integer(?MODULE:id(<<"7FFFFFFFFFFFFFFF">>), 16),

1 = Int10 rem ?MODULE:id(7),
808 = Int10 rem ?MODULE:id(1000),
8 = Int10 rem ?MODULE:id(1073741825),
-2 = Int12 rem ?MODULE:id(7),
5 = ?MODULE:id(5) rem Int13,
5 = Int13 rem ?MODULE:id(10),
42 = ?MODULE:id(42) rem Int10,
<<"7FFFFFFFFFFFFFFF">> = erlang:integer_to_binary(Int14 rem Int11, 16),
<<"8000000000000000">> = erlang:integer_to_binary(Int10 rem Int11, 16),

ok = expect_error(badarith, fun() -> Int0 rem ?MODULE:id(0) end),
ok = expect_error(badarith, fun() -> Int1 rem ?MODULE:id(0) end),
ok = expect_error(badarith, fun() -> Int10 rem ?MODULE:id(0) end),

0.

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