Add Fprint128ToBytes utility function.

PiperOrigin-RevId: 755405286

Author: nvgrw

tsl/platform/fingerprint.h

@@ -16,6 +16,10 @@ limitations under the License.
 #ifndef TENSORFLOW_TSL_PLATFORM_FINGERPRINT_H_
 #define TENSORFLOW_TSL_PLATFORM_FINGERPRINT_H_
 
+#include <array>
+#include <climits>
+#include <cstdint>
+
 #include "xla/tsl/platform/types.h"
 #include "tsl/platform/platform.h"
 #include "tsl/platform/stringpiece.h"
@@ -122,6 +126,19 @@ inline Fprint128 FingerprintCat128(const Fprint128& a, const uint64_t b) {
   return {x, FingerprintCat64(a.high64, x)};
 }
 
+inline std::array<char, 16> Fprint128ToBytes(tsl::Fprint128 fprint) {
+  static_assert(sizeof(char) == 1, "Size of char is not 1 bytes.");
+  static_assert(CHAR_BIT == 8, "Size of byte is not 8 bits.");
+  std::array<char, 16> result;
+  for (int i = 0; i < 8; ++i) {
+    result[8 - i - 1] = fprint.low64 & 0xFF;
+    result[16 - i - 1] = fprint.high64 & 0xFF;
+    fprint.low64 >>= 8;
+    fprint.high64 >>= 8;
+  }
+  return result;
+}
+
 }  // namespace tsl
 
 #endif  // TENSORFLOW_TSL_PLATFORM_FINGERPRINT_H_

tsl/platform/fingerprint_test.cc

@@ -15,6 +15,7 @@ limitations under the License.
 
 #include "tsl/platform/fingerprint.h"
 
+#include <array>
 #include <unordered_set>
 
 #include "xla/tsl/platform/test.h"
@@ -69,5 +70,14 @@ TEST(FingerprintCat64, Idempotence) {
             FingerprintCat64(Fingerprint64("Hello"), Fingerprint64("World")));
 }
 
+TEST(Fprint128ToBytes, WorksCorrectly) {
+  const Fprint128 fprint = {0xCAFEF00DDEADBEEF, 0xC0FFEE123456789A};
+  constexpr std::array<char, 16> kExpected = {
+      '\xca', '\xfe', '\xf0', '\x0d', '\xde', '\xad', '\xbe', '\xef',
+      '\xc0', '\xff', '\xee', '\x12', '\x34', '\x56', '\x78', '\x9a',
+  };
+  EXPECT_EQ(Fprint128ToBytes(fprint), kExpected);
+}
+
 }  // namespace
 }  // namespace tsl