Data Types
The dtype field in an object descriptor names the element type of the tensor. It is stored as a lowercase text string in CBOR.
Type Table
| CBOR string | Rust variant | Bytes per element | Notes |
|---|---|---|---|
float16 | Dtype::Float16 | 2 | IEEE 754 half-precision |
bfloat16 | Dtype::Bfloat16 | 2 | Brain float — same exponent range as float32, less mantissa precision |
float32 | Dtype::Float32 | 4 | IEEE 754 single-precision |
float64 | Dtype::Float64 | 8 | IEEE 754 double-precision |
complex64 | Dtype::Complex64 | 8 | Pair of float32 (real, imaginary) |
complex128 | Dtype::Complex128 | 16 | Pair of float64 (real, imaginary) |
int8 | Dtype::Int8 | 1 | Signed |
int16 | Dtype::Int16 | 2 | Signed |
int32 | Dtype::Int32 | 4 | Signed |
int64 | Dtype::Int64 | 8 | Signed |
uint8 | Dtype::Uint8 | 1 | Unsigned |
uint16 | Dtype::Uint16 | 2 | Unsigned |
uint32 | Dtype::Uint32 | 4 | Unsigned |
uint64 | Dtype::Uint64 | 8 | Unsigned |
bitmask | Dtype::Bitmask | 0* | Packed bits |
*bitmask returns 0 from byte_width() — see the edge case note below.
Byte Order
The byte_order field in the payload descriptor specifies whether multi-byte elements are stored in big-endian ("big") or little-endian ("little") order. This applies to the stored payload bytes after encoding.
Single-byte types (int8, uint8, bitmask) are unaffected by byte order.
Bitmask Edge Case
Dtype::Bitmask is for packing boolean or categorical data sub-byte. The payload size is ceil(num_elements / 8) bytes. The byte_width() method returns 0 as a sentinel; callers that need the actual payload size must compute it:
#![allow(unused)]
fn main() {
let payload_bytes = if dtype == Dtype::Bitmask {
(num_elements + 7) / 8
} else {
num_elements * dtype.byte_width()
};
}Choosing a dtype
| Situation | Recommended dtype |
|---|---|
| Temperature, wind speed, pressure (weather) | float32 |
| High-precision scientific analysis | float64 |
| ML model weights | bfloat16 or float16 |
| Integer indices, counts | int32 or int64 |
| Land-sea masks, validity flags | uint8 or bitmask |
| Complex wave spectra | complex64 |