Use different hash algorithms for strings and file hashing

For hash map, using fnv1a is faster as it is a much simpler algorithm
we can afford to inline. For files murmur3 should win as it processes
bytes 4 by 4.

src/buffer_utils.cc

@@ -140,7 +140,7 @@ decltype(auto) parse_file(StringView filename, Func&& func)
     const bool crlf = has_crlf and not has_lf;
     auto eolformat = crlf ? EolFormat::Crlf : EolFormat::Lf;
 
-    FsStatus fs_status{file.st.st_mtim, file.st.st_size, hash_data(file.data, file.st.st_size)};
+    FsStatus fs_status{file.st.st_mtim, file.st.st_size, murmur3(file.data, file.st.st_size)};
     return func(parse_lines(pos, end, eolformat), bom, eolformat, fs_status);
 }
 

src/client.cc

@@ -394,7 +394,7 @@ void Client::check_if_buffer_needs_reloading()
             return;
 
         if (MappedFile fd{filename};
-            fd.st.st_size == status.file_size and hash_data(fd.data, fd.st.st_size) == status.hash)
+            fd.st.st_size == status.file_size and murmur3(fd.data, fd.st.st_size) == status.hash)
             return;
 
         if (reload == Autoreload::Ask)

src/file.cc

@@ -626,7 +626,7 @@ FsStatus get_fs_status(StringView filename)
 {
     MappedFile fd{filename};
 
-    return {fd.st.st_mtim, fd.st.st_size, hash_data(fd.data, fd.st.st_size)};
+    return {fd.st.st_mtim, fd.st.st_size, murmur3(fd.data, fd.st.st_size)};
 }
 
 String get_kak_binary_path()

src/hash.cc

@@ -27,8 +27,8 @@ static inline uint32_t fmix(uint32_t h)
     return h;
 }
 
-// murmur3 hash, based on https://github.com/PeterScott/murmur3
+// based on https://github.com/PeterScott/murmur3
-size_t hash_data(const char* input, size_t len)
+size_t murmur3(const char* input, size_t len)
 {
     const uint8_t* data = reinterpret_cast<const uint8_t*>(input);
     uint32_t hash = 0x1235678;
@@ -73,13 +73,13 @@ size_t hash_data(const char* input, size_t len)
 UnitTest test_murmur_hash{[] {
     {
         constexpr char data[] = "Hello, World!";
-        kak_assert(hash_data(data, strlen(data)) == 0xf816f95b);
+        kak_assert(murmur3(data, strlen(data)) == 0xf816f95b);
     }
     {
         constexpr char data[] = "xxxxxxxxxxxxxxxxxxxxxxxxxxxx";
-        kak_assert(hash_data(data, strlen(data)) == 3551113186);
+        kak_assert(murmur3(data, strlen(data)) == 3551113186);
     }
-    kak_assert(hash_data("", 0) == 2572747774);
+    kak_assert(murmur3("", 0) == 2572747774);
 }};
 
 }

src/hash.hh

@@ -5,11 +5,23 @@
 #include <utility>
 
 #include <cstddef>
+#include <cstdint>
 
 namespace Kakoune
 {
 
-size_t hash_data(const char* data, size_t len);
+inline size_t fnv1a(const char* data, size_t len)
+{
+    constexpr uint32_t FNV_prime_32 = 16777619;
+    constexpr uint32_t offset_basis_32 = 2166136261;
+
+    uint32_t hash_value = offset_basis_32;
+    for (size_t i = 0; i < len; ++i)
+        hash_value = (hash_value ^ data[i]) * FNV_prime_32;
+    return hash_value;
+}
+
+size_t murmur3(const char* input, size_t len);
 
 template<typename Type> requires std::is_integral_v<Type>
 constexpr size_t hash_value(const Type& val)

src/string.hh

@@ -21,7 +21,7 @@ public:
 
     friend constexpr size_t hash_value(const Type& str)
     {
-        return hash_data(str.data(), (int)str.length());
+        return fnv1a(str.data(), (int)str.length());
     }
 
     using iterator = CharType*;