//
// This confidential and proprietary software may be used only as
// authorised by a licensing agreement from ARM Limited
// (C) COPYRIGHT 2020 ARM Limited
// ALL RIGHTS RESERVED
// The entire notice above must be reproduced on all authorised
// copies and copies may only be made to the extent permitted
// by a licensing agreement from ARM Limited.

=== Image Operators

==== RESIZE

Resizes a tensor. Resize is only allowed in the H and W dimensions.

The NEAREST_NEIGHBOR mode returns the value of the input tensor closest to the
calculated sample position for both floating point and integer data formats.

Floating point BILINEAR mode returns a bilinearly interpolated output value
based on the four closest input sample positions.

For integer BILINEAR interpolation mode, the output value is calculated by using
the shift value along with the other parameters to create a fixed point scaling
factor for each input. These values are then summed to create the value for
output, which has 2 * shift fractional bits. To convert back to the original
integer size, the output value must be rescaled.

For floating point stride, stride_y should be set to  IH/OH, stride_x should be
set to IW/OW. When using integer stride, stride_y is approximately
(IH<<shift)/OH and stride_x is approximately (IW<<shift)/OW. OH and OW are also
supplied as inputs since there may be off by one errors if calculating OH and OW
from the strides.

*Arguments:*

|===
|Argument|Type|Name|Shape|Description

|Input|in_t*|input|[N,IH,IW,C]|Input tensor
|Attribute|int*|output_size|[2]|[OH,OW]
|Attribute|resize_t*|stride|[2]|[stride_y, stride_x]
|Attribute|resize_t*|offset|[2]|[offset_y, offset_x]
|Attribute|int|shift|Shift value (must be zero if resize_t is float)
|Attribute|mode_t|mode|-|BILINEAR or NEAREST
|Output|out_t*|output|[N,OH,OW,C]|Output tensor
|===

*Quantization Parameters:*

None

*Operation Function*

[source,c]
----
// scale assert prevents int32_t accumulator overflow for in_t==int8_t
assert((resize_t==float && shift==0)||(0<shift && shift<=11));
assert(stride_x>0 && stride_y>0);
for_each (0<=n<N, 0<=oy<OH, 0<=ox<OW; 0<=c<C) {
    unit = (resize_t==float) ? 1.0 : (1<<shift);
    y = oy * stride_y + offset_y
    x = ox * stride_x + offset_x
    if (resize_t==float) {
        iy = (int)floor(y); dy = y - (float)iy;
        ix = (int)floor(x); dx = x - (float)ix;
    } else {
        iy = y >> shift; dy = y - (iy<<shift);
        ix = x >> shift; dx = x - (ix<<shift);
    }
    iy0 = apply_max(iy,0);
    iy1 = apply_min(iy+1,IH-1);
    ix0 = apply_max(ix,0);
    ix1 = apply_min(ix+1,IW-1);
    assert(ix0<=ix1 && iy0<=iy1);
    if (mode==BILINEAR) {
        v00 = tensor_read<in_t>(input, [N,IH,IW,C], [n,iy0,ix0,c])
        v01 = tensor_read<in_t>(input, [N,IH,IW,C], [n,iy0,ix1,c])
        v10 = tensor_read<in_t>(input, [N,IH,IW,C], [n,iy1,ix0,c])
        v11 = tensor_read<in_t>(input, [N,IH,IW,C], [n,iy1,ix1,c])
        out_t acc = v00*(unit-dy)*(unit-dx) + v01*(unit-dy)*dx
        acc = acc + v10*dy*(unit-dx) + v11*dy*dx;
        tensor_write<out_t>(output, [N,OH,OW,C], [n,oy,ox,c], acc)
    } else if (mode==NEAREST) {
        iy = (dy >= unit/2) ? iy1 : iy0;
        ix = (dx >= unit/2) ? ix1 : ix0;
        v = tensor_read<in_t>(input, [N,IH,IW,C], [n,iy,ix,c]);
        tensor_write<out_t>(output, [N,OH,OW,C], [n,oy,ox,c], v)
    }
}
----

*Supported Data Types:*

|===
|Profile|Mode|resize_t|in_t|out_t

|Any|signed 8,  bilinear|int16|int8|int32
|Any|signed 8,  nearest |int16|int8|int8
|Any|signed 16, bilinear|int16|int16|int48
|Any|signed 16, nearest |int16|int16|int16
|MI,MT|float            |float|float|float
|===

*Resize Modes:*
|===
|Mode|Description

|NEAREST|Nearest Neighbor
|BILINEAR|Bilinear interpoloation
|===