DX-Ball: can you hear which side the brick is on?

02. Follow the brick hit to the sound call

Start with a visible event: a brick breaks on one side of the screen. Work backward from the sound call and identify what value the caller passes. A number that looks like a coordinate could instead be a tile index, an offset or a scaled position.

Use the exact release identity in the upstream report before reusing its addresses. The reported target helper begins at 0x406400. If your executable differs, locate its corresponding behavior rather than assuming the same address works.

Inspect my matching DX-Ball 1.07 executable with REA. Start from the pan helper identified in the official report and inspect its brick-hit caller. Explain how the caller constructs the argument. Cite both call-site instructions and the helper’s input load. Do not assume the decompiler signature is complete.

03. When pseudocode loses the argument, read the instructions

A decompiler can produce a short, unhelpful body even when the machine instructions are available. Inspect the stack load, floating-point operations, referenced data and integer conversion together. Ask for the original bytes of each constant, including its type and byte order.

The documented calculation is trunc((x × 1.5625 − 500) × scale). The caller supplies horizontal position. Notice the conversion at the end: truncation toward zero matters for negative values and is different from rounding down.

• Where does the input enter the function?
• Which referenced bytes decode to each floating-point constant?
• Is scale a parameter, stored state or a fixed literal?
• Does conversion truncate, round, saturate or overflow on the tested input range?

04. Make the number audible, carefully

First implement the numeric function and check left, center and right. Then add nearby positions that produce a fraction. At x = 319 and scale = 1, the raw value is −1.5625 and the integer result is −1. A floor operation would incorrectly produce −2.

Our sound button maps pan / 500 into a Web Audio stereo panner and clamps that preview to −1…1. This makes direction easy to hear; it does not reproduce DirectSound’s volume curve or the original game audio. The displayed integer is not clamped.

Implement the documented position-to-pan calculation independently. Test x = 0, 1, 319, 320, 321 and 640 at scales 0, 0.5, 1, 20 and −1. Preserve conversion toward zero. Build a user-triggered tone preview, label its normalization separately, and never use the preview’s clipping as the recovered numeric behavior.

05. Understand what 3,205 passing checks prove

The project reports comparing 641 integer positions with five scale settings against the original x86 function. It separately reports a 63-byte compiler match in its specified historical environment. Those are two different checks: matching behavior for selected inputs, and matching generated machine code.

For your own investigation, retain each input pair and both outputs. If a mismatch appears, reduce it to the smallest failing case. Only attempt a byte match once the compiler version, options and relocation treatment are explicit. Our JavaScript tests cover the documented arithmetic; they do not repeat that original-binary comparison.