Per-Tensor Affine Quantization — Hurray Format Specification

Scheme tag: 0x01 | Tier: 1

This section uses RFC 2119 key words: MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL.

Description

A single scale and zero_point pair applies to every element of the tensor. This scheme covers both asymmetric quantization (arbitrary zero_point) and symmetric quantization (zero_point = 0).

The scale and zero-point are stored inline in the quantization descriptor; no additional buffer table entries are required beyond the tensor data buffer.

Binary Encoding

Total descriptor length: 16 bytes.

Offset	Field	Type	Description
0	`scheme_tag`	`uint8`	MUST be `0x01`.
1	`scheme_version`	`uint8`	MUST be `0x01`. For the version compatibility policy, see `quantization.md` § Version Compatibility.
2	`flags`	`uint16`	MUST be `0x0000`. No flags are defined for this scheme.
4	`scale`	`float32`	Dequantization scale. MUST be a finite, non-zero value.
8	`zero_point`	`int32`	Quantization zero point. For symmetric quantization, MUST be `0x00000000`.
12	`_reserved`	`uint8[4]`	MUST be `0x00`.

All multi-byte fields MUST be encoded in little-endian byte order.

Dequantization Formula

For each storage element q:

x_real = scale * (q - zero_point)

The subtraction q - zero_point is performed in signed 32-bit integer arithmetic. The result is then cast to float32 and multiplied by scale in float32 arithmetic. The real-valued element type produced by dequantization is float32. A consumer MAY further convert to float64 or to a lower-precision float type; such conversion is out of scope for this specification.

zero_point is subtracted exactly as stored. See quantization.md § Zero-Point Convention for the normalization a writer MUST apply when converting from a toolchain that stores a biased zero point.

Validity Constraints

scale MUST NOT be zero, NaN, or infinity. A reader MUST reject a descriptor that violates this constraint.
zero_point MUST lie within the representable range of the storage type. For example, for a uint8 storage type, zero_point MUST be in [0, 255]. A reader MUST reject a descriptor that violates this constraint.
The _reserved bytes MUST be 0x00. A reader MUST reject a descriptor that violates this constraint.

Valid Storage Types

The storage type (type_tag in the tensor descriptor) MUST be one of:

int8 (0x10), uint8 (0x11)
int16 (0x12), uint16 (0x13)
int32 (0x14), uint32 (0x15)
int4 (0x48), uint4 (0x49)
int2 (0x4A), uint2 (0x4B)

A reader MUST reject a descriptor whose storage type is not in this list.