Runtime Dispatch

Every call runs on the CPU and dispatches to the best kernel of its enabled capabilities, a BigInt bitmask a Device reports:

const cpu = sz.Device.cpu();
console.log(cpu.capabilitiesEnabled()); // what dispatch uses
console.log((cpu.capabilitiesEnabled() & sz.Capability.haswell) !== 0n);

capabilitiesEnabled() is the one you usually want, and derives from two independent axes:

• capabilitiesDetected(): what this device can execute.
• capabilitiesCompiled(): what this build contains for devices of its kind, from the ISA probes at build time.
• capabilitiesEnabled(): what dispatch uses, both axes at once.

capabilitiesDetected() describes the machine and says nothing about whether a kernel was compiled in, so a build whose ISA probes failed still reports your CPU’s full feature set while containing no SIMD kernels at all. The enabled set always keeps the serial fallback.

A Device is the host CPU or one GPU of a runtime, named by that runtime’s own ordinal:

sz.Device.count("cpu");            // 1
const gpu = new sz.Device("cuda"); // throws without a CUDA device, or past the last one
gpu.capabilitiesEnabled();         // what that GPU runs, like `Capability.cuda`

• Device.cpu() is the host CPU, which every build has.
• Device.count(kind) counts the devices of "cpu", "cuda", "rocm" or "metal", and throws without a GPU of that kind.
• new Device(kind, ordinal) throws a RangeError past the last device.

Capability maps each lowercase capability name, like haswell, neon or cuda, to its bit, and the cpus, devices and any groups to theirs. It is built at load from the C library’s own names.

There is no configure_thread call in the JS binding. Thread configuration is managed internally by the native addon.