// Two-way split/merge: merge up to 2 source buckets to up to 2 destination buckets.
// Bucket arrays are NULL-terminated.
void (*twoway_merge)(struct sort_context *ctx, struct sort_bucket **ins, struct sort_bucket **outs);
// Two-way split/merge: merge up to 2 source buckets to up to 2 destination buckets.
// Bucket arrays are NULL-terminated.
void (*twoway_merge)(struct sort_context *ctx, struct sort_bucket **ins, struct sort_bucket **outs);