CVS-183516: Fix offset & length conversion in weight sharing logic as size_t

[ankitm3k]

CVS-183516: Fix offset & length conversion in weight sharing logic as size_t

Summary

Fixes a Windows-only crash (std::out_of_range) when creating inference sessions with
OVEP weight sharing enabled on models whose external data files exceed 4.29 GB.

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Problem

During weight-sharing session creation, CreateModelWithStrippedQDQNodes iterates over
TensorProto external data entries and parses the offset and length fields — stored
as plain decimal strings per the ONNX spec — using std::stoul:

data_offset = std::stoul(pb_value);  // "offset"
size        = std::stoul(pb_value);  // "length"

On Windows, MSVC defines unsigned long as 32-bit (max 4,294,967,295 ≈ 4.29 GB).
For models like Phi-Silica PSU2, external tensor offsets into phi_36_lora_2_5_1.data_proxy
reach ~5.67 GB — well above this ceiling. std::stoul throws std::out_of_range before
any value is assigned, crashing session creation.

The target variables data_offset and size are already declared as size_t (64-bit on
x64), so the overflow happens entirely inside stoul itself.

On Linux, GCC/Clang define unsigned long as 64-bit so the bug is latent but not
triggered — however the code was still incorrect and non-portable.

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Fix

Replace std::stoul with std::from_chars from <charconv> (C++17):

#include <charconv>

std::from_chars(pb_value.data(), pb_value.data() + pb_value.size(), data_offset);
std::from_chars(pb_value.data(), pb_value.data() + pb_value.size(), size);

std::from_chars is the correct tool here for several reasons:

Property	std::stoul	std::from_chars
Parse width	unsigned long (32-bit on Windows)	Deduced from target type (size_t = 64-bit)
Error handling	Throws std::out_of_range	Returns result struct; never throws
Locale	Locale-aware (subtle portability risk)	Always locale-independent decimal
ONNX wire format	Mismatch risk	Plain decimal — exact match
Performance	Slow (locale table lookups)	Fastest standard string→integer parse

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Root Cause Chain

TensorProto::external_data[i].value()   →  std::string  (decimal, e.g. "6091128832")
std::stoul(value)                        →  unsigned long  (32-bit on MSVC)
                                         →  std::out_of_range thrown  (> 4,294,967,295)
Session creation aborts

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Files Changed

File	Change
onnxruntime/core/providers/openvino/qdq_transformations/qdq_stripping.cc	Add #include <charconv>; replace 2× std::stoul with std::from_chars targeting size_t

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Testing

Validated against Phi-Silica PSU2 with ep.share_ep_contexts=1 on Windows. Session
creation completes without std::out_of_range. No functional change on Linux.