fill_block
static void fill_block(const BLOCK *prev, const BLOCK *ref, BLOCK *next,
fill_block(zero_block, input_block, address_block, 0);
fill_block(zero_block, address_block, address_block, 0);
fill_block(ctx->memory + prev_offset, ref_block, curr_block, 0);
fill_block(ctx->memory + prev_offset, ref_block, curr_block,