Dequantize {#dev_guide_op_dequantize}
=====================================

## General

Dequantize operation converts a quantized (u8/s8/f8_e4m3/f8_e5m2) tensor to an
f32 tensor. It supports both per-tensor and per-channel asymmetric linear
de-quantization. Rounding mode is library-implementation defined. Zero points
(`zps` in the attribute table) are not supported for f8_e4m3 and f8_e5m2
dequantization.

For per-tensor de-quantization:

  \f[ \dst_{i} = round((\src_{i} - zps) \times scale) \f]

For per-channel de-quantization, taking channel axis = 1 as an example:

   \f[ dst_{\cdots,i,\cdots,\cdots} = (\src_{\cdots,i,\cdots,\cdots} - zps_i) \times scale_i, i \in {[0, ic-1]} \f]

where \f$ic\f$ is the number of channels.

## Operation attributes

| Attribute Name                               | Description                                                          | Value Type | Supported Values                                                          | Required or Optional |
|:---------------------------------------------|:---------------------------------------------------------------------|:-----------|:--------------------------------------------------------------------------|:---------------------|
| [qtype](@ref dnnl::graph::op::attr::qtype)   | Specifies which de-quantization type is used.                        |string      | `per_tensor` (default), `per_channel`                                     | Optional             |
| [axis](@ref dnnl::graph::op::attr::axis)     | Specifies dimension on which per-channel de-quantization is applied. |s64         | A s64 value in the range of [-r, r-1] where r = rank(src), `1` by default | Optional             |
| [scales](@ref dnnl::graph::op::attr::scales) | Scalings applied on the src data.                                    |f32         | A f32 list (only contain one element if qtype is `per_tensor`)            | Required             |
| [zps](@ref dnnl::graph::op::attr::zps)       | Offset values that maps to float zero.                               |s64         | A s64 list (only contain one element if qtype is `per_tensor`). If omitted, zps values are assumed to be zero. | Optional             |

## Execution arguments

The inputs and outputs must be provided according to below index order when
constructing an operation.

### Inputs

| Index | Argument Name | Required or Optional |
|:------|:--------------|:---------------------|
| 0     | `src`         | Required             |

### Outputs

| Index | Argument Name | Required or Optional |
|:------|:--------------|:---------------------|
| 0     | `dst`         | Required             |

## Supported data types

Dequantize operation supports the following data type combinations.

| Src                      | Dst |
|:-------------------------|:----|
| s8, u8, f8_e4m3, f8_e5m2 | f32 |

@note This operation is to support
[int8 quantization](@ref dev_guide_graph_int8_quantization_model) model.