Failure to round-trip roaring64 frozen bitmap

[Dr-Emann]

roaring64_bitmap_t* r1 = roaring64_bitmap_from(1, 2, 3, 4);
roaring64_bitmap_shrink_to_fit(r1);
if (!roaring64_bitmap_internal_validate(r1, &reason)) {
    fail_msg("Validation failed: %s", reason);
}
char buf[1024];
size_t alignment_offset = 32 - (reinterpret_cast<uintptr_t>(buf) % 32);
size_t buf_size = sizeof(buf) - alignment_offset;
assert_in_range(roaring64_bitmap_frozen_size_in_bytes(r1), 0, buf_size);
size_t serialized_size =
    roaring64_bitmap_frozen_serialize(r1, buf + alignment_offset);
assert_int_equal(serialized_size, roaring64_bitmap_frozen_size_in_bytes(r1));
roaring64_bitmap_t* r2 =
    roaring64_bitmap_frozen_view(buf + alignment_offset, serialized_size);
if (!roaring64_bitmap_internal_validate(r2, &reason)) {
    // Fails with "Validation failed: array elements not strictly increasing"
    fail_msg("Validation failed: %s", reason);
}
assert_true(roaring64_bitmap_equals(r1, r2));
roaring64_bitmap_free(r1);
roaring64_bitmap_free(r2);

The serialization appears to succeed, but the deserialized bitmap doesn't seem to contain the right array elements.

[Dr-Emann]

Maybe related, this one succeeds at validation, but the values aren't equal when they should be:

const char* reason = nullptr;
roaring64_bitmap_t* r1 = roaring64_bitmap_from(0x0, 0x10000, 0x1000000, 0x100000000, 0x10000000000, 0x1000000000000, 0x100000000000000, 0xfffffffffffffcff);
roaring64_bitmap_shrink_to_fit(r1);
if (!roaring64_bitmap_internal_validate(r1, &reason)) {
    fail_msg("Validation failed: %s", reason);
}
char buf[1024];
size_t alignment_offset = 32 - (reinterpret_cast<uintptr_t>(buf) % 32);
size_t buf_size = sizeof(buf) - alignment_offset;
assert_in_range(roaring64_bitmap_frozen_size_in_bytes(r1), 0, buf_size);
size_t serialized_size =
    roaring64_bitmap_frozen_serialize(r1, buf + alignment_offset);
assert_int_equal(serialized_size,
                 roaring64_bitmap_frozen_size_in_bytes(r1));
roaring64_bitmap_t* r2 =
    roaring64_bitmap_frozen_view(buf + alignment_offset, serialized_size);
if (!roaring64_bitmap_internal_validate(r2, &reason)) {
    fail_msg("Validation failed: %s", reason);
}
// Errors here, r1 != r2, but they should be.
assert_true(roaring64_bitmap_equals(r1, r2));
roaring64_bitmap_free(r1);
roaring64_bitmap_free(r2);

[Dr-Emann]

Ah. It's (at least partly) my fault: the frozen format for 32 bit bitmaps documents it requires 32 byte alignment, and I just used the same alignment here, whereas for bitmap64, we actually require 64 byte alignment.

See #698 which would have caught this much faster.