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[wasm] Fix gather operation bug when using batches #8659

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[wasm] Fix gather operation bug when using batches #8659

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c395ca3
[wasm] Fix GatherV2 batch indices bug
unexploredtest Mar 31, 2026
44a368c
[wasm] Change gather parameter name
unexploredtest Mar 31, 2026
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12 changes: 6 additions & 6 deletions tfjs-backend-wasm/src/cc/kernels/Gather.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -24,13 +24,13 @@ namespace {
template <typename T>
void gather_impl(const T* x_ptr, const std::vector<size_t>& x_strides,
const int32_t* indices_ptr, const size_t out_size,
const size_t batch_size,
const size_t indices_per_batch,
const std::vector<size_t>& out_strides, T* out_buf_ptr) {
for (size_t i = 0; i < out_size; ++i) {
auto loc = tfjs::util::offset_to_loc(i, out_strides);
const size_t batch_loc = loc[0];
const size_t indices_loc = loc[2];
loc[2] = indices_ptr[batch_loc * batch_size + indices_loc];
loc[2] = indices_ptr[batch_loc * indices_per_batch + indices_loc];

const size_t original_index = tfjs::util::loc_to_offset(loc, x_strides);

Expand All @@ -50,7 +50,7 @@ EMSCRIPTEN_KEEPALIVE

void Gather(const size_t x_id, const DType dtype, const int32_t* x_strides_ptr,
const size_t strides_size, const size_t indices_id,
const size_t batch_size, const int32_t* out_strides_ptr,
const size_t indices_per_batch, const int32_t* out_strides_ptr,
const size_t out_id) {
auto& x_info = backend::get_tensor_info(x_id);
auto& indices_info = backend::get_tensor_info(indices_id);
Expand All @@ -67,15 +67,15 @@ void Gather(const size_t x_id, const DType dtype, const int32_t* x_strides_ptr,
switch (dtype) {
case DType::float32:
gather_impl<float>(x_info.f32(), x_strides, indices_buf, out_size,
batch_size, out_strides, out_info.f32_write());
indices_per_batch, out_strides, out_info.f32_write());
break;
case DType::int32:
gather_impl<int32_t>(x_info.i32(), x_strides, indices_buf, out_size,
batch_size, out_strides, out_info.i32_write());
indices_per_batch, out_strides, out_info.i32_write());
break;
case DType::boolean:
gather_impl<bool>(x_info.b(), x_strides, indices_buf, out_size,
batch_size, out_strides, out_info.b_write());
indices_per_batch, out_strides, out_info.b_write());
break;
default:
util::warn("Gather for tensor id %d failed. Unknown dtype %d", x_id,
Expand Down
7 changes: 4 additions & 3 deletions tfjs-backend-wasm/src/kernels/GatherV2.ts
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Expand Up @@ -24,7 +24,7 @@ import {CppDType} from './types';

let wasmGather: (
xId: number, dtype: CppDType, xStrides: Uint8Array, stridesSize: number,
indicesId: number, batchSize: number, outStrides: Uint8Array,
indicesId: number, indicesPerBatch: number, outStrides: Uint8Array,
outId: number) => void;

function setup(backend: BackendWasm): void {
Expand All @@ -34,7 +34,7 @@ function setup(backend: BackendWasm): void {
'array', // xStrides
'number', // stridesSize
'number', // indicesId
'number', // batchSize
'number', // indicesPerBatch
'array', // outStrides
'number' // outId
]);
Expand Down Expand Up @@ -88,6 +88,7 @@ function gatherV2(
return out;
}
const stridesSize = flattenX.shape.length - 1;
const indicesPerBatch = indicesSize / shapeInfo.batchSize;

const xData = backend.dataIdMap.get(flattenX.dataId);
const xId = xData.id;
Expand All @@ -104,7 +105,7 @@ function gatherV2(

wasmGather(
xId, CppDType[x.dtype], xStridesBytes, stridesSize, indicesId,
shapeInfo.batchSize, outStridesBytes, outId);
indicesPerBatch, outStridesBytes, outId);

backend.disposeData(flattenX.dataId);
backend.disposeData(flattenIndex.dataId);
Expand Down