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Fix BFloat16 logits returned as garbage in Logits::Get() #2203

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Merged
kunal-vaishnavi merged 3 commits into from
Jun 18, 2026
+20 −3
Merged

Fix BFloat16 logits returned as garbage in Logits::Get() #2203

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7c912eb
Fix BFloat16 logits returned as garbage in Logits::Get()
justinchuby Jun 9, 2026
6822c1e
Apply suggestions from code review
kunal-vaishnavi Jun 9, 2026
ecb6086
Merge branch 'microsoft:main' into justinchu/bf16-logits-cast
justinchuby Jun 12, 2026
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2 changes: 2 additions & 0 deletions src/cuda/interface.cpp
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Expand Up @@ -122,6 +122,8 @@ struct CudaInterfaceImplBase : DeviceInterface {
cuda::LaunchFp32ToFp16(reinterpret_cast<const float*>(input_data), reinterpret_cast<uint16_t*>(output_data), static_cast<int>(element_count), GetStream());
} else if (input_type == Ort::TypeToTensorType<Ort::Float16_t> && output_type == Ort::TypeToTensorType<float>) {
cuda::LaunchFp16ToFp32(reinterpret_cast<const uint16_t*>(input_data), reinterpret_cast<float*>(output_data), static_cast<int>(element_count), GetStream());
} else if (input_type == Ort::TypeToTensorType<Ort::BFloat16_t> && output_type == Ort::TypeToTensorType<float>) {
cuda::LaunchBf16ToFp32(reinterpret_cast<const uint16_t*>(input_data), reinterpret_cast<float*>(output_data), static_cast<int>(element_count), GetStream());
} else if (input_type == Ort::TypeToTensorType<int32_t> && output_type == Ort::TypeToTensorType<int64_t>) {
cuda::LaunchInt32ToInt64(reinterpret_cast<const int32_t*>(input_data), reinterpret_cast<int64_t*>(output_data), static_cast<int>(element_count), GetStream());
} else
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1 change: 1 addition & 0 deletions src/cuda/kernels.h
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Expand Up @@ -13,6 +13,7 @@ void Launch_UpdateAttentionMask(T* mask_data, T* old_data, int batch_beam_size,

void LaunchAddLogitsMask(float* batch_logits, int batch_beam_size, int vocab_size, const uint32_t* logits_mask, cudaStream_t stream);
void LaunchFp16ToFp32(const uint16_t* fp16, float* fp32, int count, cudaStream_t stream);
void LaunchBf16ToFp32(const uint16_t* bf16, float* fp32, int count, cudaStream_t stream);
void LaunchFp32ToFp16(const float* fp32, uint16_t* fp16, int count, cudaStream_t stream);
void LaunchInt32ToInt64(const int32_t* src, int64_t* dst, int count, cudaStream_t stream);

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14 changes: 14 additions & 0 deletions src/cuda/model_kernels.cu
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Expand Up @@ -2,6 +2,7 @@
// Licensed under the MIT License.

#include <cuda_fp16.h>
#include <cuda_bf16.h>
#include <cuda_runtime.h>
#include <stdint.h>
#include <limits>
Expand Down Expand Up @@ -128,6 +129,19 @@ void LaunchFp32ToFp16(const float* fp32, uint16_t* fp16, int count, cudaStream_t
CUDA_CHECK_LAUNCH();
}

__global__ void ConvertBf16ToFp32(const __nv_bfloat16* src, float* dst, int count) {
int idx = threadIdx.x + blockIdx.x * blockDim.x;
if (idx < count)
dst[idx] = __bfloat162float(src[idx]);
}

void LaunchBf16ToFp32(const uint16_t* bf16, float* fp32, int count, cudaStream_t stream) {
constexpr int block_size = 256;
const int num_blocks = (count + block_size - 1) / block_size;
ConvertBf16ToFp32<<<num_blocks, block_size, 0, stream>>>(reinterpret_cast<const __nv_bfloat16*>(bf16), fp32, count);
CUDA_CHECK_LAUNCH();
}

__global__ void ConvertInt32ToInt64(const int32_t* src, int64_t* dst, int count) {
int idx = threadIdx.x + blockIdx.x * blockDim.x;
if (idx < count) {
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6 changes: 3 additions & 3 deletions src/models/logits.cpp
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Expand Up @@ -44,7 +44,7 @@ DeviceSpan<float> Logits::Get() {
// create new OrtValue for logits_of_last_token and use output_last_tokens_ to hold it
output_last_tokens_ = OrtValue::CreateTensor(model_.p_device_inputs_->GetAllocator(), shape_last, type_);

if (type_ == Ort::TypeToTensorType<Ort::Float16_t>)
if (type_ == Ort::TypeToTensorType<Ort::Float16_t> || type_ == Ort::TypeToTensorType<Ort::BFloat16_t>)
logits_of_last_token_fp32_ = OrtValue::CreateTensor<float>(model_.p_device_inputs_->GetAllocator(), shape_);
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logits_of_last_token = output_last_tokens_.get();
Expand All @@ -69,8 +69,8 @@ DeviceSpan<float> Logits::Get() {
element_count = shape_[0] * shape_[2]; // shape_[1] is now 1, so the element count must be updated
}

// Convert from float16 to float32 if necessary
if (type_ == Ort::TypeToTensorType<Ort::Float16_t>) {
// Convert from float16/bfloat16 to float32 if necessary
if (type_ == Ort::TypeToTensorType<Ort::Float16_t> || type_ == Ort::TypeToTensorType<Ort::BFloat16_t>) {
Cast(*logits_of_last_token, logits_of_last_token_fp32_, *model_.p_device_inputs_, Ort::TypeToTensorType<float>);
logits_of_last_token = logits_of_last_token_fp32_.get();
}
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