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In order to get the performance we want, the important part is that it scales based on the old size. The compiled chunk needs to not only contain the values 1 and 2, but know when to produce them so that they are printed in the right order. In main(), we call disassembleChunk() to disassemble all of the instructions in the entire chunk. And the seperate postprocessing loop reinitializes some arrays & bitmasks, essentially bruteforces a valid concrete ordering with postprocessing reconsidering degenerate cases, recomputes some counts, adjusts the schedule to (mostly) start in the correct spot, inserts MOVs in the plan where necessary, normalizes & profiles (& optionally versions) the loop, reorders the instructions to match the schedule, optionally disables future scheduling, sets a codeblock dirty flag, inserts the movs whilst rescanning dataflow, & where it couldn’t align the schedule to the start/end of the loop unrolls the selected instructions of the loop (knowing the min-iterations indicates whether this is valid). Instead of incrementing offset in the loop, Pool Table Size we let disassembleInstruction() do it for us. There isn’t much to a return instruction, so all it does is print the name of the opcode, then return the next byte offset past this instruction.

The third byte (at offset 2) is a single-byte return instruction. Each time we add a new opcode to clox, we specify what its operands look like-its instruction format. We add the constant value itself to the chunk’s constant pool. When we write a byte of code to the chunk, we need to know what source line it came from, so we add an extra parameter in the declaration of writeChunk(). Chunks contain almost all of the information that the runtime needs from the user’s source code. Given any bytecode instruction, we need to be able to determine the line of the user’s source program that it was compiled from. Given that a series of instructions often correspond to the same source line, a natural solution is something akin to run-length encoding of the line numbers. Archived from the original on 17 April 2012. Retrieved 25 December 2011. This tertiary source reuses information from other sources without citing them in detail. In clox, we’ve reduced that down to three arrays: bytes of code, constant values, and line information for debugging. Under the hood, the memory allocator maintains additional bookkeeping information for each block of heap-allocated memory, including its size.

If the new size is smaller than the existing block of memory, it simply updates the size of the block and returns the same pointer you gave it. To grow the array, first we figure out the new capacity and grow the array to that size. Given a chunk, it will print out all of the instructions in it. The first instruction iteration looks for PHI instructions to discard. This is because, as we’ll see later, instructions can have different sizes. Some machine & Assembly languages have variable-sized addressing in conditional & unconditional jumps. I’m being vague about what it means to "load" or "produce" a constant because we haven’t learned how the virtual machine actually executes code at runtime yet. In a native compiler to machine code, those bigger constants get stored in a separate "constant data" region in the binary executable. That doesn’t work well for large or variable-sized constants like strings. Likewise, we free the constants when we free the chunk. We have no human-friendly way to see what’s actually inside that chunk we made. Now that we have a rudimentary chunk structure working, let’s start making it more useful. It’s more down to player’s personal preference than a question of it being right or wrong.

The biggest question people have when choosing their pool table is what size is actually needed to play a proper game of pool at home. It’s like having a pool pro in your pocket. Fortunately, we don’t need other operations like insertion and removal. If it doesn’t, then we first need to grow the array to make room. If there isn’t room to grow the block, realloc() instead allocates a new block of memory of the desired size, copies over the old bytes, frees the old block, and then returns a pointer to the new block. The purpose of these lights is not to illuminate the room, but only the playing surface of the pool table, so they come with their own guidelines.Guidelines state that lighting should be at least 62-66 inches from the floor to the lighting fixture, and then 32-36 inches from the pool table felt. There’s not really anything useful that our VM can do if it can’t get the memory it needs, but we at least detect that and abort the process immediately instead of returning a NULL pointer and letting it go off the rails later.