[aarch64] Fix aarch64 build so that quantize_val_arm is defined (pytorch#84564)

Summary: quantize_val_arm is used in the kernels when building under aarch64

Test Plan: CI

Differential Revision: D39272746

Pull Request resolved: pytorch#84564
Approved by: https://github.com/kimishpatel

Author: psaab

aten/src/ATen/native/quantized/AffineQuantizerBase.cpp

@@ -71,6 +71,33 @@ void quantize_vec(
           (float)scale, (int32_t)zero_point, precision});
 }
 
+#if defined(__ARM_NEON__) || defined(__aarch64__)
+// For use when compiling FBGEMM on aarch64 but still supporting x86
+// intrinsics via simde
+template <typename T>
+T quantize_val_arm(
+    const float scale,
+    const int32_t zero_point,
+    const float value) {
+  constexpr int32_t qmin = std::numeric_limits<T>::min();
+  constexpr int32_t qmax = std::numeric_limits<T>::max();
+  float inv_scale = 1.0f / scale;
+  auto r = zero_point + static_cast<int32_t>(std::nearbyint(value * inv_scale));
+  r = std::max(r, qmin);
+  r = std::min(r, qmax);
+  return static_cast<T>(r);
+}
+
+template uint8_t quantize_val_arm<uint8_t>(
+    const float scale,
+    const int32_t zero_point,
+    const float value);
+template int8_t quantize_val_arm<int8_t>(
+    const float scale,
+    const int32_t zero_point,
+    const float value);
+#endif
+
 template <typename T>
 inline float dequantize_val(double scale, int64_t zero_point, T value) {
   // NOLINTNEXTLINE(cppcoreguidelines-pro-type-member-init)