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→‎Hash algorithm

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Leoetlino

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 === Hash algorithm ===
-The algorithm given on the MK8 wiki is not fully correct: it fails to account for the fact that Nintendo's algorithm uses an unsigned 32-bit integer for the hash variable, and a '''''signed'' char variable'''.
+Nintendo's algorithm uses an unsigned 32-bit integer for the hash variable. Also note that Nintendo iterates over each byte, not each string character.
-Here is more accurate implementation of the algorithm, written in C++:
+Here is an accurate implementation of the algorithm, written in C++:
 <source lang="c++">
-  const uint32_t multiplier = 0x65;
+// key is equal to 0x65
-  const char* string = "月クッパ戦Lv3(クリア後).baglshpp";
+u32 calcHash32(const sead::SafeString& str, u32 key)
-  uint32_t hash = 0;
+{
-  int i = 0;
+    const char* str_ = str.cstr();
-  while (true) {
-     char c = string[i++]; // *signed* char
+    u32 result = 0;
-    if (!c)
+    // Each character must be treated as a signed value.
-      break;
+    // The cast to s8 (not s32) is necessary to avoid unsigned conversions.
-     hash = hash * multiplier + c;
+     for (s32 i = 0; str_[i] != '\0'; i++)
-  }
+        result = result * key + s8(str_[i]);
+     return result;
+}
 </source>
-It appears that Nintendo's compiler treats a char as a signed type.
+Note that in older versions of sead, characters were not explicitly casted to <code>s8</code> so the end result would depend on the signedness of <code>char</code> (which is implementation-defined). For GHS compiled code on the Wii U, <code>char</code> is unsigned whereas it's signed with Clang (AArch64 target). PC tools most likely use a signed <code>char</code> as that is the default signedness for x86 targets.
+In newer versions of sead, an explicit cast to <code>signed char</code>, aka <code>std::int8_t</code>, aka <code>s8</code>, was added to ensure hashes are the same regardless of the target platform. Without the cast, non-ASCII characters (e.g. Japanese UTF-8 bytes) would result in hashes being different across platforms.
 == Usage in ''Breath of the Wild'' ==