From ea7f446ac7f29fbbde579513ee52f0943b8889a7 Mon Sep 17 00:00:00 2001
From: Arne Juul <arnej@verizonmedia.com>
Date: Tue, 23 Mar 2021 12:24:11 +0000
Subject: ensure vespa BFloat16 and onnxruntime BFloat16 behave the same

---
 vespalib/src/tests/util/bfloat16/CMakeLists.txt    |  2 +
 vespalib/src/tests/util/bfloat16/bfloat16_test.cpp | 89 +++++++++++++++++++++-
 2 files changed, 90 insertions(+), 1 deletion(-)

diff --git a/vespalib/src/tests/util/bfloat16/CMakeLists.txt b/vespalib/src/tests/util/bfloat16/CMakeLists.txt
index 39a42e6f148..1916c7bb365 100644
--- a/vespalib/src/tests/util/bfloat16/CMakeLists.txt
+++ b/vespalib/src/tests/util/bfloat16/CMakeLists.txt
@@ -5,5 +5,7 @@ vespa_add_executable(vespalib_bfloat16_test_app TEST
     DEPENDS
     vespalib
     GTest::GTest
+    EXTERNAL_DEPENDS
+    onnxruntime
 )
 vespa_add_test(NAME vespalib_bfloat16_test_app COMMAND vespalib_bfloat16_test_app)
diff --git a/vespalib/src/tests/util/bfloat16/bfloat16_test.cpp b/vespalib/src/tests/util/bfloat16/bfloat16_test.cpp
index 5d70c95b1d9..a9d2ab0b8d4 100644
--- a/vespalib/src/tests/util/bfloat16/bfloat16_test.cpp
+++ b/vespalib/src/tests/util/bfloat16/bfloat16_test.cpp
@@ -5,8 +5,9 @@
 #include <vespa/vespalib/gtest/gtest.h>
 #include <stdio.h>
 #include <cmath>
-#include <cmath>
 #include <vector>
+#include <onnxruntime/core/session/onnxruntime_cxx_api.h>
+#include <onnxruntime/onnxruntime_cxx_api.h>
 
 using namespace vespalib;
 
@@ -165,4 +166,90 @@ TEST(BFloat16Test, check_special_values) {
     EXPECT_EQ(memcmp(&f_snan, &f_from_b_snan, sizeof(float)), 0);
 }
 
+#include <onnxruntime/core/framework/endian.h>
+
+// extract from onnx-internal header file:
+namespace onnxruntime {
+
+//BFloat16
+struct BFloat16 {
+  uint16_t val{0};
+  explicit BFloat16() = default;
+  explicit BFloat16(uint16_t v) : val(v) {}
+  explicit BFloat16(float v) {
+    if (endian::native == endian::little) {
+      std::memcpy(&val, reinterpret_cast<char*>(&v) + sizeof(uint16_t), sizeof(uint16_t));
+    } else {
+      std::memcpy(&val, &v, sizeof(uint16_t));
+    }
+  }
+
+  float ToFloat() const {
+    float result;
+    char* const first = reinterpret_cast<char*>(&result);
+    char* const second = first + sizeof(uint16_t);
+    if (endian::native == endian::little) {
+      std::memset(first, 0, sizeof(uint16_t));
+      std::memcpy(second, &val, sizeof(uint16_t));
+    } else {
+      std::memcpy(first, &val, sizeof(uint16_t));
+      std::memset(second, 0, sizeof(uint16_t));
+    }
+    return result;
+  }
+
+  operator float() const {
+    return ToFloat();
+  }
+};
+
+}  // namespace onnxruntime
+
+TEST(OnnxBFloat16Test, has_same_encoding) {
+    vespalib::BFloat16 our_value;
+    uint32_t ok_count = 0;
+    uint32_t nan_count = 0;
+    for (uint32_t i = 0; i < (1u << 16u); ++i) {
+        uint16_t bits = i;
+        our_value.assign_bits(bits);
+        onnxruntime::BFloat16 their_value(bits);
+        if (our_value.get_bits() != bits) {
+            printf("bad bits %04x -> %04x (vespalib)\n", bits, our_value.get_bits());
+            printf("onnx converts -> %04x\n", their_value.val);
+            EXPECT_EQ(our_value.get_bits(), their_value.val);
+            continue;
+        }
+        EXPECT_EQ(their_value.val, bits);
+        if (their_value.val != bits) {
+            printf("bad bits %04x -> %04x (onnx)\n", bits, their_value.val);
+            continue;
+        }
+        EXPECT_EQ(our_value.get_bits(), their_value.val);
+        if (our_value.get_bits() != their_value.val) {
+            printf("vespalib bits %04x != %04x onnx bits\n", our_value.get_bits(), their_value.val);
+            printf("corresponds to floats %g and %g\n", our_value.to_float(), their_value.ToFloat());
+            continue;
+        }
+        float our_float = our_value.to_float();
+        float their_float = their_value.ToFloat();
+        EXPECT_EQ(std::isnan(our_float), std::isnan(their_float));
+        if (std::isnan(our_float) && std::isnan(their_float)) {
+            ++nan_count;
+            continue;
+        } 
+        if (our_float != their_float) {
+            printf("bits %04x as float differs: vespalib %g != %g onnx\n", bits, our_value.to_float(), their_value.ToFloat());
+        } else {
+            ++ok_count;
+        }
+        EXPECT_EQ(our_float, their_float);
+        vespalib::BFloat16 our_back(our_float);
+        onnxruntime::BFloat16 their_back(their_float);
+        EXPECT_EQ(our_back.get_bits(), their_back.val);
+    }
+    printf("normal floats behave equally OK in both vespalib and onnx: %d (0x%04x)\n", ok_count, ok_count);
+    printf("floats that are NaN in both vespalib and onnx: %d (0x%04x)\n", nan_count, nan_count);
+    printf("total count (OK + NaN): %d (0x%04x)\n", ok_count + nan_count, ok_count + nan_count);
+}
+
 GTEST_MAIN_RUN_ALL_TESTS()
-- 
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