pw_random: Fix implicit conversions in RandomGenerator

Fix implicit conversion from int to uint8_t in
RandomGenerator::CountLeadingZeros. This conversion is safe because
the __builtin_clz functions always return a positive value <= 64.

This fixed compilation on Fuchsia.

Test: pw watch
Change-Id: Id7e29f80607e160c0315512aa9fca8da013cb90b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126510
Reviewed-by: Ali Zhang <[email protected]>
Commit-Queue: Ben Lawson <[email protected]>

pw_random/public/pw_random/random.h

@@ -96,16 +96,17 @@ class RandomGenerator {
   template <class T>
   uint8_t CountLeadingZeros(T value) {
     if constexpr (std::is_same_v<T, unsigned>) {
-      return __builtin_clz(value);
+      return static_cast<uint8_t>(__builtin_clz(value));
     } else if constexpr (std::is_same_v<T, unsigned long>) {
-      return __builtin_clzl(value);
+      return static_cast<uint8_t>(__builtin_clzl(value));
     } else if constexpr (std::is_same_v<T, unsigned long long>) {
-      return __builtin_clzll(value);
+      return static_cast<uint8_t>(__builtin_clzll(value));
     } else {
       static_assert(sizeof(T) < sizeof(unsigned));
       // __builtin_clz returns the count of leading zeros in an unsigned , so we
       // need to subtract the size difference of T in bits.
-      return __builtin_clz(value) - ((sizeof(unsigned) - sizeof(T)) * CHAR_BIT);
+      return static_cast<uint8_t>(__builtin_clz(value) -
+                                  ((sizeof(unsigned) - sizeof(T)) * CHAR_BIT));
     }
   }
 };